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Abstract:

[Problem] To provide a large hydraulic excavator permitting an easy change
from a machine mode corresponding to a backhoe excavator to a machine
mode corresponding to a loader excavator, and vice versa.
[MEANS for Solving the Problem] Arranged are a hydraulic circuit 1
provided with hydraulic pumps 11-18 and directional control valves 21-35,
solenoid valves 41-43, 51-66 for controlling hydraulic pumps 11-18 and
the directional control valves 21-35, and a controller 70 for controlling
the solenoid valves 41-43, 51-66 in accordance with operation of control
lever devices 80-83 and control pedal devices 84-87. The controller 70
performs control of the solenoid valves 41-43, 51-66 in a backhoe mode or
loader mode selectively instructed by a mode instruction means 71.
Control of the solenoid valves 41-43, 51-66 in the backhoe mode makes the
hydraulic circuit 1 function as a hydraulic drive circuit for backhoe,
while control of the solenoid valves 41-43, 51-66 in the loader mode
makes the hydraulic circuit 1 function as a hydraulic drive circuit for
the loader mode.

Claims:

1. A hydraulic drive system for a large hydraulic excavator, comprising:a
hydraulic circuit comprising at least two variable-displacement hydraulic
pumps and at least seven directional control valves, said hydraulic
circuit being for arrangement on a revolving upperstructure of said large
hydraulic excavator such that a hydraulic drive circuit for a backhoe
excavator, which comprises said at least two variable-displacement
hydraulic pumps and at least six of said directional control valves to
form a flow of pressure oil required for driving a right travel motor, a
left travel motor, a swing motor, a boom cylinder, an arm cylinder and a
bucket cylinder provided on said large backhoe excavator and a hydraulic
drive circuit for a loader excavator, which comprises said at least two
variable-displacement hydraulic pumps and said at least seven directional
control valves to form a flow of pressure oil required for driving a
right travel motor, a left travel motor, a swing motor, a boom cylinder,
an arm cylinder, a bucket cylinder and an open/close cylinder provided on
said large loader excavator, can be selectively controlled,a pump
flow-rate control means for controlling flow rates of said at least two
variable-displacement hydraulic pumps, respectively,a directional control
means for controlling valve positions of said at least seven directional
control valves, respectively,a regulation means for performing control of
said pump flow-rate control means and said directional control means in
one mode selected from predetermined at least two modes, anda mode
instruction means for instructing said one mode to be selected by said
regulation means from said at least two modes,wherein said at least two
modes comprises a backhoe mode, in which said pump flow-rate control
means and said directional control means are controlled to make said
hydraulic circuit function as said hydraulic drive circuit for said
backhoe excavator, and a loader mode, in which said pump flow-rate
control means and said directional control means are controlled to make
said hydraulic circuit function as said hydraulic drive circuit for said
loader excavator.

2. A hydraulic drive system according to claim 1, wherein:regulators that
make pump flow rates in said variable-displacement hydraulic pumps
variable comprise hydraulic pilot-operated regulators,said pump flow-rate
control means comprises plural flow-rate control solenoid valves arranged
such that pilot pressures can be applied to said regulators for said
respective variable-displacement hydraulic pumps,said directional control
valves comprise hydraulic pilot-operated directional control valves,said
directional control means comprises plural directional control solenoid
valves arranged such that pilot pressures can be applied to said
respective directional control valves,said regulation means has a
computer that realizes control of said pump flow-rate control means and
directional control valve control means in each of said at least two
modes by electronic control of said plural flow-rate control solenoid
valves and plural directional-control solenoid valves, andsaid mode
instruction means has an electric circuit for generating an electric
signal that instructs the kind of said mode, which is to be selected from
said at least two modes, to said computer.

3. A hydraulic drive system according to claim 2, wherein:said at least
two variable-displacement hydraulic pumps comprise first to eighth
variable-displacement hydraulic pumps, and these first to eighth
variable-displacement hydraulic pumps are grouped into a first pump unit
composed of the first variable-displacement hydraulic pump and the second
variable-displacement hydraulic pump, a second pump unit composed of the
third variable-displacement hydraulic pump and the fourth
variable-displacement hydraulic pump, a third pump unit composed of the
fifth variable-displacement hydraulic pump and the sixth
variable-displacement hydraulic pump, and a fourth pump unit composed of
the seventh variable-displacement hydraulic pump and the eighth
variable-displacement hydraulic pump,said at least seven directional
control valves comprise first to fifteenth directional control valves,
and these first to fifteenth directional control valves are grouped into
a first valve group composed of the first to fourth directional control
valves, a second valve group composed of the fifth to eighth directional
control valves, a third valve group composed of the ninth to eleventh
directional control valves, and a fourth valve group composed of the
twelfth to fifteenth directional control valves,to these first to fourth
valve groups, said first to fourth pump units are connected,
respectively, via lines each of which combines together said two
variable-displacement hydraulic pumps that make up the corresponding pump
unit,said first, fifth and fourteenth directional control valves are
arranged such that selective switching of flow rate and flow direction of
pressure oil corresponding to each of an extension and a retraction of
said boom cylinder provided on said backhoe excavator and selective
switching of flow rate and flow direction of pressure oil corresponding
to each of an extension and a retraction of said boom cylinder provided
on said loader excavator can be performed,said second, sixth and
thirteenth directional control valves are arranged such that selective
switching of flow rate and flow direction of pressure oil corresponding
to each of an extension and a retraction of said bucket cylinder provided
on said backhoe excavator and selective switching of flow rate and flow
direction of pressure oil corresponding to each of an extension and a
retraction of said bucket cylinder provided on said loader excavator can
be performed,said third and seventh directional control valves are
arranged such that selective switching of flow rate and flow direction of
pressure oil corresponding to each of an extension and a retraction of
said arm cylinder provided on said backhoe excavator and selective
switching of flow rate and flow direction of pressure oil corresponding
to each of an extension and a retraction of said arm cylinder provided on
said loader excavator can be performed,said fourth directional control
valve is arranged such that selective switching of flow rate and flow
direction of pressure oil corresponding to each of rotations in opposite
two directions of said left travel motor provided on said backhoe
excavator and selective switching of flow rate and flow direction of
pressure oil corresponding to each of rotations in opposite two
directions of said left travel motor provided on said loader excavator
can be performed,said eighth directional control valve is arranged such
that selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension and a retraction of said open/close
cylinder provided on said loader excavator can be performed,said ninth
directional control valve is arranged such that selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension of said bucket cylinder provided on said backhoe excavator and
an extension of said arm cylinder provided on said backhoe excavator and
selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension of said bucket cylinder provided on
said loader excavator and an extension of said arm cylinder provided on
said loader excavator can be performed,said tenth directional control
valve is arranged such that selective switching of flow rate and flow
direction of pressure oil corresponding to each of rotations in opposite
two directions of said swing motor provided on said backhoe excavator and
selective switching of flow rate and flow direction of pressure oil
corresponding to each of rotations in opposite two directions of said
swing motor provided on said loader excavator can be performed,said
eleventh directional control valve is arranged such that selection of
flow rate and flow direction of pressure oil corresponding to only an
extension of the extension and a retraction of said boom cylinder
provided on said backhoe excavator and selection of only an extension of
the extension and a retraction of said boom cylinder provided on said
loader excavator can be performed,said twelfth directional control valve
is arranged such that selective switching of flow rate and flow direction
of pressure oil corresponding to each of rotations in opposite two
directions of said right travel motor provided on said backhoe excavator
and selective switching of flow rate and flow direction of pressure oil
corresponding to each of rotations in opposite two directions of said
right travel motor provided on said loader excavator can be
performed,said fifteenth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension and a retraction of said arm
cylinder provided on said backhoe excavator out of said backhoe excavator
and loader excavator can be performed,said plural flow-rate control
solenoid valves comprise first, second and third flow-rate control
solenoid valves, said first flow-rate control solenoid valve is arranged
such that pilot pressures can be applied to only regulators for the
first, third, fifth, sixth, seventh and eighth variable-displacement
hydraulic pumps out of regulators for said first to eighth
variable-displacement hydraulic pumps, said second flow-rate control
solenoid valve is arranged such that a pilot pressure can be applied to
only a regulator for the second variable-displacement hydraulic pump out
of said regulators for said first to eighth variable-displacement
hydraulic pumps, and said third flow-rate control solenoid valve is
arranged such that a pilot pressure can be applied to only a regulator
for the fourth variable-displacement hydraulic pump out of said
regulators for said first to eighth variable-displacement hydraulic
pumps.

4. A hydraulic drive system according to claim 2, wherein:said at least
two variable-displacement hydraulic pumps comprise first to sixth
variable-displacement hydraulic pumps, and these first to sixth
variable-displacement hydraulic pumps are grouped into a first pump unit
composed of the first variable-displacement hydraulic pump and the second
variable-displacement hydraulic pump, a second pump unit composed of the
third variable-displacement hydraulic pump and the fourth
variable-displacement hydraulic pump, and a third pump unit composed of
the fifth variable-displacement hydraulic pump and the sixth
variable-displacement hydraulic pump,said at least seven directional
control valves comprise first to twelfth directional control valves, and
these first to twelfth directional control valves are grouped into a
first valve group composed of the first to fourth directional control
valves, a second valve group composed of the fifth to eighth directional
control valves, and a third valve group composed of the ninth to twelfth
directional control valves,to these first to third valve groups, said
first, second and third pump units are connected, respectively, via lines
each of which combines together said two variable-displacement hydraulic
pumps that make up the corresponding pump unit,said first and eleventh
directional control valves are arranged such that selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension and a retraction of said bucket cylinder provided on said
backhoe excavator and selective switching of flow rate and flow direction
of pressure oil corresponding to each of an extension and a retraction of
said bucket cylinder provided on said loader excavator can be
performed,said second and twelfth directional control valves are arranged
such that selective switching of flow rate and flow direction of pressure
oil corresponding to each of an extension and a retraction of said boom
cylinder provided on said backhoe excavator and selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension and a retraction of said boom cylinder provided on said loader
excavator can be performed,said third and fifth directional control
valves are arranged such that selective switching of flow rate and flow
direction of pressure oil corresponding to each of an extension and a
retraction of said arm cylinder provided on said backhoe excavator and
selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension and a retraction of said arm
cylinder provided on said loader excavator can be performed,said fourth
directional control valve is arranged such that selective switching of
flow rate and flow direction of pressure oil corresponding to each of
rotations in opposite two directions of said left travel motor provided
on said backhoe excavator and selective switching of flow rate and flow
direction of pressure oil corresponding to each of rotations in opposite
two directions of said left travel motor provided on said loader
excavator can be performed,said sixth directional control valve is
arranged such that selective switching of flow rate and flow direction of
pressure oil corresponding to each of an extension and a retraction of
said bucket cylinder provided on said backhoe excavator and selective
switching of flow rate and flow direction of pressure oil corresponding
to each of an extension and a retraction of said open/close cylinder
provided on said loader excavator can be performed,said seventh
directional control valve is arranged such that selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension and a retraction of said boom cylinder provided on said backhoe
excavator and selective switching of flow rate and flow direction of
pressure oil corresponding to each of an extension and a retraction of
said bucket cylinder provided on said loader excavator can be
performed,said eighth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of rotations in opposite two directions of said
right travel motor provided on said backhoe excavator and selective
switching of flow rate and flow direction of pressure oil corresponding
to each of rotations in opposite two directions of said right travel
motor provided on said loader excavator can be performed,said ninth
directional control valve is arranged such that selective switching of
flow rate and flow direction of pressure oil corresponding to each of
rotations in opposite two directions of said swing motor provided on said
backhoe excavator and selective switching of flow rate and flow direction
of pressure oil corresponding to each of rotations in opposite two
directions of said swing motor provided on said loader excavator can be
performed,said tenth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension and a retraction of said arm
cylinder provided on said backhoe excavator and selection of flow rate
and flow direction of pressure oil corresponding to only an extension of
the extension and a retraction of said arm cylinder provided on said
loader excavator can be performed, andsaid plural flow-rate control
solenoid valves comprise first, second and third flow-rate control
solenoid valves, said first flow-rate control solenoid valve is arranged
such that a pilot pressure can be applied to only a regulator for the
first variable-displacement hydraulic pump out of regulators for said
first to sixth variable-displacement hydraulic pumps, said second
flow-rate control solenoid valve is arranged such that pilot pressures
can be applied to only regulators for the second, third and fourth
variable-displacement hydraulic pumps out of said regulators for said
first to sixth variable-displacement hydraulic pumps, and said third
flow-rate control solenoid valve is arranged such that pilot pressures
can be applied to only regulators for the fifth and sixth
variable-displacement hydraulic pumps out of said regulators for said
first to sixth variable-displacement hydraulic pumps.

5. A hydraulic drive system according to claim 2, wherein:said electric
circuit is provided with a first signal generation circuit for generating
a backhoe mode selection signal that instructs selection of said backhoe
mode, a first connector capable of switching on/off said first signal
generation circuit, a second signal generation circuit for generating a
loader mode selection signal that instructs selection of said loader
mode, and a second connector capable of switching on/off said second
signal generation circuit.

6. A hydraulic drive system according to claim 5, wherein:said computer is
configured to perform mode setting by performing reading of said backhoe
mode selection signal and loader mode selection signal only once before
control of said plural flow-rate control solenoid valve and control of
said directional control solenoid valves are first initiated during from
power on to power off.

7. A hydraulic drive system according to claim 6, wherein:said hydraulic
drive system is provided with a display means for displaying results of
said reading of said backhoe mode selection signal and loader mode
selection signal,said at least two kinds of modes comprise an error mode
in which control is performed to prevent operation of said plural
flow-rate control solenoid valves and plural directional control solenoid
valves, andsaid computer is configured to set the mode in said error mode
when said results of said reading are results that said backhoe mode
selection signal and said loader mode selection signal have been both
read or when said results of said reading are results that neither said
backhoe mode selection signal nor said loader mode selection signal has
been read.

Description:

TECHNICAL FIELD

[0001]This relates to a hydraulic drive system for a large hydraulic
excavator which can be transported in a divided condition and can then be
assembled at a location close to a work site.

BACKGROUND ART

[0002]A large backhoe excavator (which may hereinafter be called simply "a
backhoe") is provided with a travel base capable of traveling by drive of
left and right crawler tracks, a revolving upperstructure mounted for
revolution on the travel base and having an operator's cab, and a front
working assembly having a boom connected to a front part of the revolving
upperstructure, an arm pivotally connected to the boom and a bucket
pivotally connected to the arm.

[0003]The backhoe excavator is also provided with plural hydraulic
actuators for driving the travel base, revolving upperstructure and front
working assembly, specifically a right travel motor and a left travel
motor as drive sources for the travel base, a swing motor as a drive
source for the revolving upperstructure, a boom cylinder as a drive
source for the boom, an arm cylinder as a drive source for the arm, and a
bucket cylinder as a drive source for the bucket.

[0004]Arranged in the operator's cab of the backhoe excavator are plural
control devices, specifically a right travel control pedal device for
instructing operation (operation direction and operation speed) of the
right travel motor, a left travel control pedal device for instructing
operation of the left travel motor, a swing control lever device for
instructing operation of the swing motor, a boom control lever device for
instructing operation of the boom cylinder, an arm control lever device
for instructing operation of the arm cylinder, and a bucket control lever
device for instructing operation of the bucket.

[0005]The backhoe excavator is further provided with a hydraulic drive
system for operating plural hydraulic actuators, namely, the right travel
motor, left travel motor, swing motor, boom cylinder, arm cylinder and
bucket cylinder in accordance with operation of the right travel control
pedal device, left travel control pedal device, swing control lever
device, boom control lever device, arm control lever device and bucket
control lever device. This hydraulic drive system is provided with a
hydraulic drive circuit including plural variable-displacement hydraulic
pumps capable of serving as hydraulic sources for the hydraulic actuators
and directional control valves interposed between said plural
variable-displacement hydraulic pumps and said plural hydraulic actuators
to control flows of pressure oil between the individual
variable-displacement hydraulic pumps and the individual hydraulic
actuators. In other words, the hydraulic drive system is configured to
control the operation directions and operation speeds of the plural
hydraulic actuators by controlling regulators for the plural
variable-displacement hydraulic pumps and the plural directional control
valves in accordance with the operation of the right travel control pedal
device, left travel control pedal device, swing control lever device,
boom control lever device, arm control lever device and bucket control
lever device.

[0006]A large loader excavator (which may hereinafter be called simply "a
loader excavator") is provided, similar to the backhoe excavator, with a
travel base, a revolving upperstructure and a front working assembly, a
right travel motor, a left travel motor, a swing motor, a boom cylinder,
an arm cylinder and a bucket cylinder as drive sources for them, and a
hydraulic drive system for controlling operation of these hydraulic
actuators.

[0007]As the front working assembly of the backhoe excavator and that of
the loader excavator are different in digging operation, the arm cylinder
and bucket cylinder are arranged on an outer side of the front working
assembly in the backhoe excavator while the arm cylinder and bucket
cylinder are arranged on an inner side of the front working assembly in
the loader excavator. As a consequence, the pivoting directions of the
arm and bucket when the arm cylinder and bucket cylinder extend or
retract in the backhoe excavator and those of the arm and bucket when the
arm cylinder and bucket cylinder extend or retract in the loader
excavator are opposite. In addition, the front working assemblies are
also different in the manner of control of flow rates suited for the
control of operation speeds.

[0008]Further, the bucket of the loader excavator is constructed openably
and closably. This bucket is provided with an open/close cylinder as a
drive source for the opening/closing of the bucket. Arranged in an
operator's cab of the loader excavator are an open control pedal device
for instructing a bucket-opening operation and a close control pedal
device for instructing a bucket-closing operation. The hydraulic drive
system of the loader excavator is constructed such that like the
hydraulic drive system of the backhoe excavator, the right travel motor,
left travel motor, swing motor, boom cylinder, arm cylinder and bucket
cylinder can be operated in accordance with the operation of the right
travel control pedal device, left travel control pedal device, swing
control lever device, boom control lever device, arm control lever device
and bucket control lever device and in addition, such that the open/close
cylinder can be operated in accordance with the operation of the open
control pedal device or close control pedal device.

[0009]As a further large hydraulic excavator constructed like the large
backhoe excavator and large loader excavator mentioned above, there is
one disclosed in Patent Document 1.

[0010]It is to be noted that the kind of large hydraulic excavators to be
manufactured is determined to that of those shipped more between backhoe
excavators and loader excavators and such large hydraulic excavators may
be kept in stock. Subsequently, each large hydraulic excavator is
transported in a divided condition to a work site where digging work or
the like is to be performed, and is then assembled into the kind ordered
by the customer. The kind of a hydraulic excavator ordered by each
customer may be different from that of a hydraulic excavator manufactured
or kept in stock. As a consequence, it becomes necessary to change the
kind of the hydraulic excavator from a backhoe excavator to a loader
excavator or from a loader excavator to a backhoe excavator in the
assembly stage of the hydraulic excavator. When changing the kind of a
hydraulic excavator as mentioned above, the progress of work at the work
site will be substantially delayed from the work schedule if the change
is dealt with by doing the fabrication and transportation again from the
beginning with respect to all the components of the hydraulic excavator.
Accordingly, the change of the hydraulic excavator is conducted by using
as many components as possible from the hydraulic excavator before the
change, and the thus-changed hydraulic excavator is then delivered.

[0011]When changing a hydraulic excavator, which is to be used at a work
site, from a backhoe excavator to a loader excavator, for example, the
travel base and swing upperstructure and the components of the hydraulic
drive system, said components being associated with these travel base and
swing upperstructure, that is, the right travel control pedal device,
left travel control pedal device, swing control lever device, boom
control lever device, arm control lever device and bucket control lever
device, all of which exist as components of the backhoe excavator, can be
used as they are, and an open control pedal device and a close control
pedal device are newly arranged. The front working assembly is replaced
by a front working assembly for loader excavator, and following this
replacement, the boom cylinder, arm cylinder and bucket cylinders are
also replaced by those corresponding to the loader excavator. An
open/close cylinder which is not arranged in the front working assembly
for the backhoe excavator is attached to the bucket. Further, the
components of the hydraulic drive system, said components being
associated with the front working assembly, are modified such that the
replaced boom cylinder, arm cylinder and bucket cylinder can be operated
in accordance with operation of the existing right travel control pedal
device, existing left travel control pedal device, existing swing control
lever device, existing boom control lever device, existing arm control
lever device and existing bucket control lever device and also, such that
the newly-arranged open/close cylinder can be operated in accordance with
operation of the newly-arranged open control pedal and newly-arranged
close control pedal.

Patent Document: JP-A-2004-100154

DISCLOSURE OF THE INVENTION

Means to be Solved by the Invention

[0012]Upon changing the kind of a large hydraulic excavator, which is to
be used at a work site, from a backhoe excavator to a loader excavator or
from a loader excavator to a backhoe excavator at the time of its
assembly, a need arises to change the components of the hydraulic drive
system, said components being associated with the front working assembly,
as mentioned above.

[0013]Whichever of the above-described changes is to be performed, it is
necessary to change the components of the hydraulic drive system, said
components being associated with the front working assembly, such that
the replaced hydraulic cylinders can be operated in accordance with
operation of the existing control lever devices. Especially when changing
from the backhoe excavator to the loader excavator, a need arises to
change the components of the hydraulic drive system, said components
being associated with the front working assembly, such that the
open/close cylinder can be operated in accordance with operation of the
open control pedal device or close control pedal device. The work to
perform such changes to the components of the hydraulic drive system,
said components being associated with the front working assembly, have
been cumbersome.

[0014]An object of the present invention is to provide a hydraulic drive
system for a large hydraulic excavator, said hydraulic drive system
permitting an easy change from one corresponding to a backhoe excavator
to one corresponding to a loader excavator or vice versa.

Means for Solving the Problems

[0015][1] This invention is characterized by comprising a hydraulic
circuit comprising at least two variable-displacement hydraulic pumps and
at least seven directional control valves, said hydraulic circuit being
for arrangement on a revolving upperstructure of the large hydraulic
excavator such that a hydraulic drive circuit for a backhoe excavator,
which comprises the at least two variable-displacement hydraulic pumps
and at least six of the directional control valves to form a flow of
pressure oil required for driving a right travel motor, a left travel
motor, a swing motor, a boom cylinder, an arm cylinder and a bucket
cylinder provided on the large backhoe excavator and a hydraulic drive
circuit for a loader excavator, which comprises the at least two
variable-displacement hydraulic pumps and the at least seven directional
control valves to form a flow of pressure oil required for driving a
right travel motor, a left travel motor, a swing motor, a boom cylinder,
an arm cylinder, a bucket cylinder and an open/close cylinder provided on
the large loader excavator, can be selectively controlled, a pump
flow-rate control means for controlling flow rates of the at least two
variable-displacement hydraulic pumps, respectively, a directional
control means for controlling valve positions of the at least seven
directional control valves, respectively, a regulation means for
performing control of the pump flow-rate control means and the
directional control means in one mode selected from predetermined at
least two modes, and a mode instruction means for instructing the one
mode to be selected by the regulation means from the at least two modes,
wherein the at least two modes comprises a backhoe mode, in which the
pump flow-rate control means and the directional control means are
controlled to make the hydraulic circuit function as the hydraulic drive
circuit for the backhoe excavator, and a loader mode, in which the pump
flow-rate control means and the directional control means are controlled
to make the hydraulic circuit function as the hydraulic drive circuit for
the loader excavator.

[0016]According to the present invention constructed as described above,
owing to the arrangement of the hydraulic circuit that can selectively
construct the hydraulic drive circuit for the backhoe excavator or the
hydraulic drive circuit for the loader excavator, it is unnecessary to
change the numbers and arrangements of the variable-displacement
hydraulic pumps and directional control valves upon changing the
hydraulic drive circuit of the large hydraulic excavator from the
hydraulic drive circuit for the backhoe excavator to the hydraulic drive
circuit for the loader excavator or from the hydraulic drive circuit for
the loader excavator to the hydraulic drive circuit for the backhoe
excavator. Further, by instructing the selection of the backhoe mode to
the regulation means from the mode instruction means, it become possible
to control the flow-rate control means and directional control means such
that the hydraulic circuit can function as the hydraulic drive circuit
for the backhoe excavator. Furthermore, by instructing the selection of
the loader mode to the regulation means from the mode instruction means,
it becomes possible to control the flow-rate control means and
directional control means such that the hydraulic circuit can function as
the hydraulic drive circuit for the loader excavator. Owing to these, it
is possible to achieve the above-mentioned object, that is, the provision
of a hydraulic drive system for a large hydraulic excavator, said
hydraulic drive system permitting an easy change from one corresponding
to a backhoe excavator to one corresponding to a loader excavator or vice
versa.

[2] The present invention may be characterized in that in the invention as
described in [1], regulators that make pump flow rates in the
variable-displacement hydraulic pumps variable comprise hydraulic
pilot-operated regulators, the pump flow-rate control means comprises
plural flow-rate control solenoid valves arranged such that pilot
pressures can be applied to the regulators for the respective
variable-displacement hydraulic pumps, the directional control valves
comprise hydraulic pilot-operated directional control valves, the
directional control means comprises plural directional control solenoid
valves arranged such that pilot pressures can be applied to the
respective directional control valves, the regulation means has a
computer that realizes control of the pump flow-rate control means and
directional control valve control means in each of the at least two modes
by electronic control of the plural flow-rate control solenoid valves and
plural directional-control solenoid valves, and the mode instruction
means has an electric circuit for generating an electric signal that
instructs the kind of the mode, which is to be selected from the at least
two modes, to the computer.[3] The present invention may be constructed
as the followings (1) to (14) in the invention as described in [1].

[0017](1) The at least two variable-displacement hydraulic pumps comprise
first to eighth variable-displacement hydraulic pumps, and these first to
eighth variable-displacement hydraulic pumps are grouped into a first
pump unit composed of the first variable-displacement hydraulic pump and
the second variable-displacement hydraulic pump, a second pump unit
composed of the third variable-displacement hydraulic pump and the fourth
variable-displacement hydraulic pump, a third pump unit composed of the
fifth variable-displacement hydraulic pump and the sixth
variable-displacement hydraulic pump, and a fourth pump unit composed of
the seventh variable-displacement hydraulic pump and the eighth
variable-displacement hydraulic pump,

[0018](2) The at least seven directional control valves comprise first to
fifteenth directional control valves, and these first to fifteenth
directional control valves are grouped into a first valve group composed
of the first to fourth directional control valves, a second valve group
composed of the fifth to eighth directional control valves, a third valve
group composed of the ninth to eleventh directional control valves, and a
fourth valve group composed of the twelfth to fifteenth directional
control valves,

[0019](3) To these first to fourth valve groups, the first to fourth pump
units are connected, respectively, via lines each of which combines
together the two variable-displacement hydraulic pumps that make up the
corresponding pump unit,

[0020](4) The first, fifth and fourteenth directional control valves are
arranged such that selective switching of flow rate and flow direction of
pressure oil corresponding to each of an extension and a retraction of
the boom cylinder provided on the backhoe excavator and selective
switching of flow rate and flow direction of pressure oil corresponding
to each of an extension and a retraction of the boom cylinder provided on
the loader excavator can be performed,

[0021](5) The second, sixth and thirteenth directional control valves are
arranged such that selective switching of flow rate and flow direction of
pressure oil corresponding to each of an extension and a retraction of
the bucket cylinder provided on the backhoe excavator and selective
switching of flow rate and flow direction of pressure oil corresponding
to each of an extension and a retraction of the bucket cylinder provided
on the loader excavator can be performed,

[0022](6) The third and seventh directional control valves are arranged
such that selective switching of flow rate and flow direction of pressure
oil corresponding to each of an extension and a retraction of the arm
cylinder provided on the backhoe excavator and selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension and a retraction of the arm cylinder provided on the loader
excavator can be performed,

[0023](7) The fourth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of rotations in opposite two directions of the left
travel motor provided on the backhoe excavator and selective switching of
flow rate and flow direction of pressure oil corresponding to each of
rotations in opposite two directions of the left travel motor provided on
the loader excavator can be performed,

[0024](8) The eighth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension and a retraction of the open/close
cylinder provided on the loader excavator can be performed,

[0025](9) The ninth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension of the bucket cylinder provided on
the backhoe excavator and an extension of the arm cylinder provided on
the backhoe excavator and selective switching of flow rate and flow
direction of pressure oil corresponding to each of an extension of the
bucket cylinder provided on the loader excavator and an extension of the
arm cylinder provided on the loader excavator can be performed,

[0026](10) The tenth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of rotations in opposite two directions of the
swing motor provided on the backhoe excavator and selective switching of
flow rate and flow direction of pressure oil corresponding to each of
rotations in opposite two directions of the swing motor provided on the
loader excavator can be performed,

[0027](11) The eleventh directional control valve is arranged such that
selection of flow rate and flow direction of pressure oil corresponding
to only an extension of the extension and a retraction of the boom
cylinder provided on the backhoe excavator and selection of only an
extension of the extension and a retraction of the boom cylinder provided
on the loader excavator can be performed,

[0028](12) The twelfth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of rotations in opposite two directions of the
right travel motor provided on the backhoe excavator and selective
switching of flow rate and flow direction of pressure oil corresponding
to each of rotations in opposite two directions of the right travel motor
provided on the loader excavator can be performed,

[0029](13) The fifteenth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension and a retraction of the arm
cylinder provided on the backhoe excavator out of the backhoe excavator
and loader excavator can be performed,

[0030](14) The plural flow-rate control solenoid valves comprise first,
second and third flow-rate control solenoid valves, the first flow-rate
control solenoid valve is arranged such that pilot pressures can be
applied to only regulators for the first, third, fifth, sixth, seventh
and eighth variable-displacement hydraulic pumps out of regulators for
the first to eighth variable-displacement hydraulic pumps, the second
flow-rate control solenoid valve is arranged such that a pilot pressure
can be applied to only a regulator for the second variable-displacement
hydraulic pump out of the regulators for the first to eighth
variable-displacement hydraulic pumps, and the third flow-rate control
solenoid valve is arranged such that a pilot pressure can be applied to
only a regulator for the fourth variable-displacement hydraulic pump out
of the regulators for the first to eighth variable-displacement hydraulic
pumps.

[4] The present invention may be constructed as the followings (1) to (13)
in the invention as described in [1].

[0031](1) The at least two variable-displacement hydraulic pumps comprise
first to sixth variable-displacement hydraulic pumps, and these first to
sixth variable-displacement hydraulic pumps are grouped into a first pump
unit composed of the first variable-displacement hydraulic pump and the
second variable-displacement hydraulic pump, a second pump unit composed
of the third variable-displacement hydraulic pump and the fourth
variable-displacement hydraulic pump, and a third pump unit composed of
the fifth variable-displacement hydraulic pump and the sixth
variable-displacement hydraulic pump,

[0032](2) The at least seven directional control valves comprise first to
twelfth directional control valves, and these first to twelfth
directional control valves are grouped into a first valve group composed
of the first to fourth directional control valves, a second valve group
composed of the fifth to eighth directional control valves, and a third
valve group composed of the ninth to twelfth directional control valves,

[0033](3) To these first to third valve groups, the first, second and
third pump units are connected, respectively, via lines each of which
combines together the two variable-displacement hydraulic pumps that make
up the corresponding pump unit,

[0034](4) The first and eleventh directional control valves are arranged
such that selective switching of flow rate and flow direction of pressure
oil corresponding to each of an extension and a retraction of the bucket
cylinder provided on the backhoe excavator and selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension and a retraction of the bucket cylinder provided on the loader
excavator can be performed,

[0035](5) The second and twelfth directional control valves are arranged
such that selective switching of flow rate and flow direction of pressure
oil corresponding to each of an extension and a retraction of the boom
cylinder provided on the backhoe excavator and selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension and a retraction of the boom cylinder provided on the loader
excavator can be performed,

[0036](6) The third and fifth directional control valves are arranged such
that selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension and a retraction of the arm
cylinder provided on the backhoe excavator and selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension and a retraction of the arm cylinder provided on the loader
excavator can be performed,

[0037](7) The fourth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of rotations in opposite two directions of the left
travel motor provided on the backhoe excavator and selective switching of
flow rate and flow direction of pressure oil corresponding to each of
rotations in opposite two directions of the left travel motor provided on
the loader excavator can be performed,

[0038](8) The sixth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension and a retraction of the bucket
cylinder provided on the backhoe excavator and selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension and a retraction of the open/close cylinder provided on the
loader excavator can be performed,

[0039](9) The seventh directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension and a retraction of the boom
cylinder provided on the backhoe excavator and selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension and a retraction of the bucket cylinder provided on the loader
excavator can be performed,

[0040](10) The eighth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of rotations in opposite two directions of the
right travel motor provided on the backhoe excavator and selective
switching of flow rate and flow direction of pressure oil corresponding
to each of rotations in opposite two directions of the right travel motor
provided on the loader excavator can be performed,

[0041](11) The ninth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of rotations in opposite two directions of the
swing motor provided on the backhoe excavator and selective switching of
flow rate and flow direction of pressure oil corresponding to each of
rotations in opposite two directions of the swing motor provided on the
loader excavator can be performed,

[0042](12) The tenth directional control valve is arranged such that
selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension and a retraction of the arm
cylinder provided on the backhoe excavator and selection of flow rate and
flow direction of pressure oil corresponding to only an extension of the
extension and a retraction of the arm cylinder provided on the loader
excavator can be performed, and

[0043](13) The plural flow-rate control solenoid valves comprise first,
second and third flow-rate control solenoid valves, the first flow-rate
control solenoid valve is arranged such that a pilot pressure can be
applied to only a regulator for the first variable-displacement hydraulic
pump out of regulators for the first to sixth variable-displacement
hydraulic pumps, the second flow-rate control solenoid valve is arranged
such that pilot pressures can be applied to only regulators for the
second, third and fourth variable-displacement hydraulic pumps out of the
regulators for the first to sixth variable-displacement hydraulic pumps,
and the third flow-rate control solenoid valve is arranged such that
pilot pressures can be applied to only regulators for the fifth and sixth
variable-displacement hydraulic pumps out of the regulators for the first
to sixth variable-displacement hydraulic pumps.

[5] The present invention may be characterized in that in the invention as
described in [2], the electric circuit is provided with a first signal
generation circuit for generating a backhoe mode selection signal that
instructs selection of the backhoe mode, a first connector capable of
switching on/off the first signal generation circuit, a second signal
generation circuit for generating a loader mode selection signal that
instructs selection of the loader mode, and a second connector capable of
switching on/off the second signal generation circuit.

[0044]According to the present invention constructed as described above,
the mode can be set in the backhoe mode by bringing the second connector
into a disconnected state while maintaining the first connector in a
connected state, and further, the mode can be set for the loader
excavator by bringing the second connector into a connected state while
maintaining the first connector in a disconnected state. Therefore, the
mode can be changed by the simple work that each connector is pulled out
or pushed in, so that the mode can be changed with ease. In addition, the
first and second signal generation circuits are electric circuits of
simple construction so that troubles can be readily found and their
maintenance is easy.

[6] The present invention may be characterized in that in the invention as
described in [5], the computer is configured to perform mode setting by
performing reading of the backhoe mode selection signal and loader mode
selection signal only once before control of the plural flow-rate control
solenoid valve and control of the directional control solenoid valves are
first initiated during from power on to power off.

[0045]According to the present invention constructed as described above,
even if a disconnection or short-circuit occurs in the first signal
generation circuit or second signal generation circuit during work by the
hydraulic excavator, it is possible to avoid such a situation that the
mode is changed from the backhoe mode to the loader mode or from the
loader mode to the backhoe mode. It is, therefore, possible to avoid a
faulty operation of the hydraulic excavator, which would otherwise be
caused by a disconnection or short-circuit in the first signal generation
circuit or second signal generation circuit.

[7] The present invention may be characterized in that in the invention as
described in [6], the at least two kinds of modes comprise an error mode
in which control is performed to prevent operation of the plural
flow-rate control solenoid valves and plural directional control solenoid
valves, the computer is configured to set the mode in the error mode when
the results of the reading are results that the backhoe mode selection
signal and the loader mode selection signal have been both read or when
the results of the reading are results that neither the backhoe mode
selection signal nor the loader mode selection signal has been read, and
the hydraulic drive system is provided with a display means for
displaying the results of the reading.

[0046]According to the present invention constructed as described above,
it is possible to confirm, by looking at the display of the display
means, whether or not the results of the reading of the backhoe mode
selection signal or loader mode selection signal by the computer are the
results corresponding to the states of the first and second connectors.
As a consequence, the present invention can contribute to the detection
of a mix-up of the states of the first and second connectors
corresponding to each of the backhoe mode and loader mode and also to the
detection of a disconnection or short-circuit in the first or second
signal generation circuit.

Advantageous Effects of the Invention

[0047]According to the present invention, it is possible, as mentioned
above, to provide a hydraulic drive system for a large hydraulic
excavator, said hydraulic drive system permitting an easy change from one
corresponding to a backhoe excavator to one corresponding to a loader
excavator or vice versa. Therefore, the labor required for the
above-described changing work can be reduced, and further, the time
required for the work can be shortened.

BEST MODES FOR CARRYING OUT THE INVENTION

[0048]A description will be made about a large hydraulic excavator to
which embodiments of the present invention for the large hydraulic
excavator can be applied.

[0049]FIG. 1 is a side view of a large backhoe excavator to which the
embodiments of the present invention can be applied.

[0050]The backhoe excavator 200 depicted in FIG. 1 is provided with a
travel base 201 capable of traveling by drive of left and right crawler
tracks, a revolving upperstructure 202 mounted for revolution as a main
unit of the backhoe excavator 200 on the travel base 201 and having an
operator's cab 202a, and a front working assembly 203 having a boom 204
connected to a front part of the revolving upperstructure 202, an arm 205
pivotally connected to the boom 204 and a bucket 206 pivotally connected
to the arm 205.

[0051]The backhoe excavator 200 is provided with a right travel motor (not
shown) and a left travel motor (not shown) as drive sources for the
travel base 201, a swing motor (not shown) as a drive source for the
revolving upperstructure 202, a boom cylinder 207 as a drive source for
the boom 204, an arm cylinder 208 as a drive source for the arm 205, and
a bucket cylinder 209 as a drive source for the bucket 206.

[0052]Arranged in the operator's cab 202a of the backhoe excavator 200 are
plural control devices (not shown), specifically a right travel control
pedal device for instructing operation (operation direction and operation
speed) of the right travel motor, a left travel control pedal device for
instructing operation of the left travel motor, a swing control lever
device for instructing operation of the swing motor, a boom control lever
device for instructing operation of the boom cylinder 207, an arm control
lever device for instructing operation of the arm cylinder 208, and a
bucket control lever device for instructing operation of the bucket
cylinder 209.

[0053]The revolving upperstructure 202 of the backhoe excavator 200 is
further provided with a hydraulic drive system (not shown) for
controlling operation of the right travel motor, left travel motor, swing
motor, boom cylinder 207, arm cylinder 208 and bucket cylinder 209 in
accordance with individual instructions (control signals) from the right
travel control pedal device, left travel control pedal device, swing
control lever device, boom control lever device, arm control lever device
and bucket control lever device.

[0054]FIG. 2 is a side view of a large loader excavator to which the
embodiment of the present invention is applied.

[0055]The large loader excavator 300 depicted in FIG. 2 is provided with a
travel base 301, a revolving upperstructure 302 and a front working
assembly 303, plural hydraulic actuators for driving them, specifically a
right travel motor (not shown), a left travel motor (not shown), a swing
motor (not shown), a boom cylinder 307, an arm cylinder 308 and a bucket
cylinder 309, and a hydraulic drive system (not shown) for controlling
operation of these hydraulic actuators.

[0056]In the loader excavator 300, the travel base 301 and revolving
upperstructure 302 and the components of the hydraulic drive circuit,
said components being for driving the right travel motor, left travel
motor and swivel motor, are constructed as in the above-mentioned large
backhoe excavator 200 depicted in FIG. 1. The boom 304, arm 305 and
bucket 306 in the front working assembly 303 of the loader excavator 300
have different constructions from the above-mentioned corresponding ones
depicted in FIG. 1.

[0057]As already described in the Background Art, the front working
assembly 203 of the backhoe excavator 200 and the front working assembly
303 of the loader excavator 300 are different in digging operation so
that the arm cylinder 208 and bucket cylinder 209 are arranged on an
outer side of the front working assembly 203 in the backhoe excavator 200
while the arm cylinder 308 and bucket cylinder 309 are arranged on an
inner side of the front working assembly 303 in the loader excavator 300.
As a consequence, the pivoting directions of the arm 205 and bucket 209
when the arm cylinder 208 and bucket cylinder 209 extend or retract in
the backhoe excavator 200 and those of the arm 305 and bucket 306 when
the arm cylinder 308 and bucket cylinder 309 extend or retract in the
loader excavator 300 are opposite. In addition, the front working
assembly 203 and the front working assembly 303 are also different in the
manner of control of flow rates suited for the control of operation
speeds.

[0058]Further, the bucket 306 in the front working assembly 303 of the
loader excavator 303 is constructed openably and closably. This bucket
306 is provided with an open/close cylinder 313 as a drive source for
opening/closing operation. Arranged in an operator's cab 302a of the
loader excavator 300 are an open control pedal device (not shown) for
instructing operation to open the bucket 306 and a close control pedal
device (not shown) for instructing operation to close the bucket 306, and
the open control pedal device and close control pedal device are
constructed similar to the above-mentioned right travel control pedal
deice. The hydraulic drive system of the loader excavator 300 is
constructed such that like the hydraulic drive system of the backhoe
excavator 200, the right travel motor, left travel motor, swing motor,
boom cylinder 307, arm cylinder 308 and bucket cylinder 309 can be
operated in accordance with the operation of the right travel control
pedal device, left travel control pedal device, swing control lever
device, boom control lever device, arm control lever device and bucket
control lever device and in addition, such that the open/close cylinder
313 can be operated in accordance with the operation of the open control
pedal device or close control pedal device.

First Embodiment

[0059]A description will be made about a first embodiment of the present
invention.

[0060]FIG. 3 is a diagram illustrating a state that a hydraulic circuit
arranged in the first embodiment of the hydraulic drive system of this
invention for the large hydraulic excavator is connected to the left
travel motor, right travel motor, swing motor, boom cylinder, arm
cylinder and bucket cylinder arranged on the backhoe excavator. FIG. 4 is
a diagram showing a state that the hydraulic circuit depicted in FIG. 3
is connected to the left travel motor, right travel motor, swingmotor,
boom cylinder, arm cylinder, bucket cylinder and open/close cylinder
arranged on the loader excavator.

[0061]As illustrated in these FIGS. 3 and 4, the first embodiment is
provided with a hydraulic circuit 1 including at least two
variable-displacement hydraulic pumps and at least seven directional
control valves, for example, 1st-8th variable-displacement
hydraulic pumps 11-18 and 1st-15th directional control valves
21-35 arranged on the revolving upperstructure of the large hydraulic
excavator such that they can selectively construct a hydraulic drive
circuit for the backhoe excavator to drive the boom cylinder 207, bucket
cylinder 209, arm cylinder 208, left travel motor 210, swing motor 211
and right travel motor 212 arranged on the backhoe excavator 200 or a
hydraulic drive circuit for the loader excavator to drive the boom
cylinder 307, bucket cylinder 309, arm cylinder 308, open/close cylinder
313, left travel motor 310, swing motor 311 and right travel motor 312
arranged on the loader excavator 300.

[0063]Also in FIGS. 3 and 4, BMU, BMD, BKC, BKD, AMC, AMD, SR, SL, TRF,
TRB, TLF, TLB, DO and DC are signs that designate pilot pressures to be
applied to the 1st-15th directional control valves 31-35. These
signs have the following meanings: [0064]BMU: A pilot pressure
corresponding to extensions of the boom cylinders 207, 307 [0065]BMD: A
pilot pressure corresponding to retractions of the boom cylinders 207,
307 [0066]BKC: A pilot pressure corresponding to extensions of the bucket
cylinders 209, 309 [0067]BKD: A pilot pressure corresponding to
retractions of the bucket cylinders 209, 309 [0068]AMC: A pilot pressure
corresponding to extensions of the arm cylinders 208, 308 [0069]AMD: A
pilot pressure corresponding to retractions of the arm cylinders 208, 308
[0070]SR: A pilot pressure corresponding to rotations of the swing motors
211, 311 in rightward swinging directions [0071]SL: A pilot pressure
corresponding to rotations of the swing motors 211, 311 in leftward
swinging directions [0072]TRF: A pilot pressure corresponding to
rotations of the right travel motors 212, 312 in advancing directions
[0073]TRB: A pilot pressure corresponding to rotations of the right
travel motors 212, 312 in reversing directions [0074]TLF: A pilot
pressure corresponding to rotations of the left travel motors 210, 310 in
advancing directions [0075]TLB: A pilot pressure corresponding to
rotations of the left travel motors 210, 310 in reversing directions
[0076]DO: A pilot pressure corresponding to a retraction of the
open/close cylinder 313 [0077]DC: A pilot pressure corresponding to an
extension of the open/close cylinder 313

[0079]The 1st-15th directional control valves 21-35 are grouped
into a 1st valve group 6 comprised of the 1st-4th
directional control valves 21-24, a 2nd valve group 7 comprised of
the 5th-8th directional control valves 25-28, a 3rd valve
group 8 comprised of the 9th-11th directional control valves
29-31, and a 4th valve group 9 comprised of the 12th-15th
directional control valves 32-35.

[0080]To these 1st-4th valve groups 6-9, the 1st-4th
pump units 2-5 are connected, respectively, via lines each of which
combines together oils delivered from the two variable-displacement
hydraulic pumps that make up the corresponding pump unit, that is, lines
36, 36, 37, 38.

[0081]The 1st, 5th and 14th directional control valves 21,
25, 34 are arranged such that they can perform selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension and a retraction of the boom cylinder 207 arranged on the
backhoe excavator 200 and selective switching of flow rate and flow
direction of pressure oil corresponding to each of an extension and a
retraction of the boom cylinder 307 arranged on the loader excavator 300.

[0082]The 2nd, 6th and 13th directional control valves 22,
26, 33 are arranged such that they can perform selective switching of
flow rate and flow direction of pressure oil corresponding to each of an
extension and a retraction of the bucket cylinder 209 arranged on the
backhoe excavator 200 and selective switching of flow rate and flow
direction of pressure oil corresponding to each of an extension and a
retraction of the bucket cylinder 309 arranged on the loader excavator
300.

[0083]The 3rd and 7th directional control valves 23, 27 are
arranged such that they can perform selective switching of flow rate and
flow direction of pressure oil corresponding to each of an extension and
a retraction of the arm cylinder 208 arranged on the backhoe excavator
200 and selective switching of flow rate and flow direction of pressure
oil corresponding to each of an extension and a retraction of the arm
cylinder 308 arranged on the loader excavator 300.

[0084]The 4th directional control valve 24 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to each of rotations in opposite two
directions of the left travel motor 210 arranged on the backhoe excavator
200 and selective switching of flow rate and flow direction of pressure
oil corresponding to each of rotations in opposite two directions of the
left travel motor 310 arranged on the loader excavator 300.

[0085]The 8th directional control valve 28 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to each of an extension and a retraction of
the open/close cylinder 313 arranged on the loader excavator 300.

[0086]The 9th directional control valve 29 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to each of an extension of the bucket cylinder
209 arranged on the backhoe excavator 200 and an extension of the arm
cylinder 208 arranged on the backhoe excavator 200 and selective
switching of flow rate and flow direction of pressure oil corresponding
to each of an extension of the bucket cylinder 309 arranged on the loader
excavator 300 and an extension of the arm cylinder 308 arranged on the
loader excavator 300.

[0087]The 10th directional control valve 30 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to each of rotations in opposite two
directions of the swing motor 211 arranged on the backhoe excavator 200
and selective switching of flow rate and flow direction of pressure oil
corresponding to each of rotations in opposite two directions of the
swing motor 311 arranged on the loader excavator 300.

[0088]The 11th directional control valve 31 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to only an extension out of the extension and
a retraction of the boom cylinder 207 arranged on the backhoe excavator
200 and selective switching of flow rate and flow direction of pressure
oil corresponding to only an extension out of the extension and a
retraction of the boom cylinder 307 arranged on the loader excavator 300.

[0089]The 12th directional control valve 32 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to each of rotations in opposite two
directions of the right travel motor 212 arranged on the backhoe
excavator 200 and selective switching of flow rate and flow direction of
pressure oil corresponding to each of rotations in opposite two
directions of the right travel motor 312 arranged on the loader excavator
300.

[0090]The 15th directional control valve 35 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to each of an extension and a retraction of
the arm cylinder 208 arranged on the backhoe excavator 200 out of the
backhoe excavator 200 and loader excavator 300.

[0091]FIG. 5 is a block diagram illustrating a system which the first
embodiment is provided with to control the hydraulic circuits shown in
FIGS. 3 and 4.

[0092]In this FIG. 5, designated at 80-87 are control devices all arranged
in the operator's cab 203a of the backhoe excavator 200 or the operator's
cab 303a of the loader excavator 303, specifically a boom control lever
device 80, a bucket control lever device 81, an arm control lever device
82, a swing control lever device 83, a right travel control pedal device
84, a left travel control pedal device 85, an open control pedal device
86, and a close control pedal device 87. It is to be noted that the open
control pedal device 86 and close control pedal device 87 are arranged
only in the operator's cab 303a of the loader excavator 300.

[0093]The boom control level device 80 is provided with a control lever
80a arranged pivotally in two opposite directions from a neutral position
and an angle detector 80b for outputting a control signal (electrical
signal) corresponding to a pivot angle (operation direction and operation
stroke) of the control lever 80a. The control signal indicates a pivot
angle of the control lever 80a by a voltage value of, for example, from
-2.5 to 2.5V. Described specifically, the voltage value of the control
signal becomes 0 V when the control lever 80a is at the neutral position,
becomes a voltage value higher than 0 V, with 2.5 V being the upper
limit, when the control lever 80a is pivoted in one direction from the
neutral position, and becomes a voltage value lower than 0 V, with -2.5 V
being the lower limit, when the control lever 80a is pivoted in an
opposite direction from the neutral position. The bucket control lever
device 81, arm control lever device 82 and swing control lever device 83
are also constructed like the boom control lever device 80.

[0094]The right travel control pedal device 84 is provided with a control
pedal 84a arranged pivotally in two opposite directions from a neutral
position and an angle detector 84b for outputting a control signal
(electrical signal) corresponding to a pivot angle (operation direction
and operation stroke) of the control pedal 84a. The left travel control
pedal device 85, open control pedal device 86 and close control pedal
device 87 are also constructed like the right travel control pedal device
84. Control signals from these right travel control pedal device 84, left
travel control pedal device 85, open control pedal device 86 and close
control pedal device 87 are also electrical signals similar to the
above-mentioned control signal from the boom control lever device 80.

[0095]The first embodiment is provided with 1st, 2nd and
3rd flow-rate control solenoid valves 41, 42, 43 arranged such that
the pilot pressures i1-i8 can be applied to the pump flow rate control
means for controlling the pump flow rates of the respective
1st-8th variable-displacement hydraulic pumps 11-18, for
example, the regulators 11a-18a for the 1st-8th
variable-displacement hydraulic pumps 11-18. The first embodiment is also
provided with a direction control means for controlling the respective
1st-15th directional control valves 21-35, for example,
1st-16th directional control solenoid valves 51-66 arranged
such that the pilot pressures BMU, BMD, BKC, BKD, AMC, AMD, SR, SL, TRF,
TRB, TLF, TLB, DO, DC can be applied to the 1st-15th
directional control valves 21-35. The first embodiment is further
provided with a pilot pump 73 as a hydraulic pressure source for the
pilot pressures i1-i8 and the pilot pressures BMU, BMD, BKC, BKD, AMC,
AMD, SR, SL, TRF, TRB, TLF, TLB, DO, DC. The 1st, 2nd and
3rd flow-rate control solenoid valves 41, 42, 43 and the
1st-16th directional control solenoid valves 51-66 are
comprised of proportional solenoid control valves.

[0096]The 1st flow-rate control solenoid valve 41 is arranged such
that pilot pressures can be applied to only the regulators 11a, 13a, 15a,
16a, 17a, 18a for the 1st, 3rd, 5th, 6th, 7th
and 8th variable-displacement hydraulic pumps 11, 13, 15, 16, 17, 18
out of the regulators 11a-18a for the 1st-8th
variable-displacement hydraulic pumps 11-18. The 2nd flow-rate
control solenoid valve 42 is arranged such that a pilot pressure can be
applied to only the regulator 12a for the 2nd variable-displacement
hydraulic pump 12 out of the regulators 11a-18a for the 1st-8th
variable-displacement hydraulic pumps 11-18. The 3rd flow-rate
control solenoid valve 43 is arranged such that a pilot pressure can be
applied to only the regulator 14a for the 4th variable-displacement
hydraulic pump 14 out of the regulators 11a-18a for the 1st-8th
variable-displacement hydraulic pumps 11-18.

[0097]The 1st directional control solenoid valve 51 is arranged such
that the pilot pressure BMU can be applied to the 1st, 5th,
11th and 14th directional control valves 21, 25, 31, 34. The
2nd directional control solenoidvalve 52 is arranged such that the
pilot pressure BMD can be applied to the 1st, 5th and 14th
directional control valves 21, 25, 34.

[0098]The 3rd directional control solenoid valve 53 is arranged such
that the pilot pressure BKC can be applied to the 2nd, 6th,
9th and 13th directional control valves 22, 26, 29, 33. The
4th directional control solenoid valve 54 is arranged such that the
pilot pressure BKD can be 22, 26, 33.

[0099]The 5th directional control solenoid valve 55 is arranged such
that the pilot pressure AMC can be applied to the 3rd, 7th and
9th directional control valves 22, 27, 29. The 6th directional
control solenoid valve 56 is arranged such that the pilot pressure AMD
can be applied to the 3rd and 7th directional control solenoid
valves 23, 27.

[0100]The 7th directional control solenoid valve 57 is arranged such
that the pilot pressure AMC can be applied to the 15th directional
control valve 35. The 8th directional control solenoid valve 58 is
arranged such that the pilot pressure AMD can be applied to the 15th
directional control valve 35.

[0101]The 9th directional control solenoid valve 59 is arranged such
that the pilot pressure SR can be applied to the 10th directional
control valve 30. The 10th directional control solenoid valve 60 is
arranged such that the pilot pressure SL can be applied to the 10th
directional control valve 30.

[0102]The 11th directional control solenoid valve 61 is arranged such
that the pilot pressure TRF can be applied to the 12th directional
control valve 32. The 12th directional control solenoid valve 62 is
arranged such that the pilot pressure TRB can be applied to the 12th
directional control valve 32.

[0103]The 13th directional control solenoid valve 63 is arranged such
that the pilot pressure TLF can be applied to the 4th directional
control valve 24. The 14th directional control solenoid valve 64 is
arranged such that the pilot pressure TLB can be applied to the 4th
directional control valve 24.

[0104]The 15th directional control solenoid valve 65 is arranged such
that the pilot pressure DO can be applied to the 8th directional
control valve 28. The 16th directional control solenoid valve 66 is
arranged such that the pilot pressure DC can be applied to the 8th
directional control valve 28.

[0105]The first embodiment is provided with a controller 70 as a
regulation means for performing control of the pump flow-rate control
means and directional control means in one mode selected from
predetermined at least two modes. This controller 70 has a computer,
which realizes by electronic control the control of the 1st,
2nd and 3rd flow-rate control solenoid valves 41, 42, 43 as the
pump flow-rate control means and the 1st-16th directional
control solenoid valves 51-66 as the directional control means. This
computer is configured to perform the control of the 1st, 2nd
and 3rd flow-rate control solenoid valves 41, 42, 43 and
1st-15th directional control solenoid valves 51-66 in
accordance with control signals from the boom control lever device 80,
bucket control lever device 81, arm control lever device 82, swing
control lever device 83, right travel control pedal device 84, left
travel control pedal device 85, open control pedal device 86, and close
control pedal device 87.

[0106]The first embodiment is provided with a mode instruction means 71
for instructing a mode to be selected by the regulation means. This mode
instruction means 71 has an electric circuit for generating an electrical
signal that instructs the kind of a mode, which is to be selected from at
least two kinds of modes, to the computer of the controller 70.

[0107]The at least two kinds of modes include three kinds of modes, that
is, a backhoe mode, a loader mode and an error mode. The backhoe mode is
a mode in which the control of the 1st, 2nd and 3rd
flow-rate control solenoid valves 41, 42, 43 and 1st-16th
directional control solenoid valves 51-66 is performed to make the
hydraulic circuit 1 function as a hydraulic drive circuit for the backhoe
excavator. The loader mode is a mode in which the control of the
1st, 2nd and 3rd flow-rate control solenoid valves 41, 42,
43 and 1st-16th directional control solenoid valves 51-66 is
performed to make the hydraulic circuit 1 function as a hydraulic drive
circuit for the loader excavator. The error mode is a mode in which the
1st, 2nd and 3rd flow-rate control solenoid valves 41, 42,
43 and the 1st-16th directional control solenoid valves 51-66
are both controlled to remain inoperative.

[0109]The controller 70 is configured to perform mode setting by
performing reading of the backhoe mode selection signal B and loader mode
selection signal L only once before the control of the 1st, 2nd
and 3rd flow-rate control solenoid valves 41, 42, 43 and the
1st-16th directional control solenoid valves 51-66 are first
initiated during from power on to power off.

[0110]To the controller 70, a display unit 72 is connected. The controller
70 is set to output an instruction signal to the display unit 72 such
that the display unit 72 shows the results of reading of the backhoe mode
selection signal B and loader mode selection signal L. Therefore, the
first embodiment is provided with a display means for showing the results
of reading of the backhoe mode selection signal B and loader mode
selection signal L. The display unit 72 is arranged in the operator's cab
202a of the backhoe excavator 200 or the operator's cab 302a of the
loader mode 300.

[0111]The computer of the controller 70 is configured to set the mode in
the error mode when the results of reading of the backhoe mode selection
signal B and loader mode selection signal L are the results that both of
the backhoe mode selection signal B and loader mode selection signal L
have been read or the results that neither the backhoe mode selection
signal B nor the loader mode selection signal L has been read.

[0112]FIG. 6 is a diagram illustrating processing which the controller
depicted in FIG. 5 performs to control the 1st and 2nd
directional control solenoid valves.

[0113]As illustrated in FIG. 6, the controller 70 is set to perform
processing Pbm1, Pbm2 when a control signal is inputted from the boom
control lever device 80.

[0114]The processing Pbm1 comprises the processing that selectively
performs the first or second processing to be described next in (1) and
(2).

[0115](1) The first processing is the processing that, when the condition
that the voltage value of a control signal is 0 V or higher (control
signal≧0 (positive)) is satisfied, the voltage value of the
control signal is substituted for the value indicating an operation
stroke Vbm1 of the control lever 80a upon the pivotal operation of the
control lever 80a in the one direction from the neutral position
(operation stroke Vbm1=control signal, operation stroke Vbm2=0 (zero)).

[0116](2) The second processing is the processing that, when the condition
that the voltage value of a control signal is lower than 0 (control
signal<0 (negative)) is satisfied, the absolute value (ABS) of the
voltage value of the control signal is substituted for the value
indicating the operation stroke Vbm2 upon the pivotal operation of the
control lever 80a in the other direction (the direction opposite to the
one direction) from the neutral position (operation stroke Vbm1=0 (zero),
operation stroke Vbm2=control signal (ABS)).

[0117]The processing Pbm2 consists of a processing that calculates a
target control amount for the 1st directional control solenoid valve
51, that is, the value of a current (solenoid valve current Abm1) to be
applied to the 1st directional control solenoid valve 51 on the
basis of the value of the operation stroke Vbm1 obtained in the
processing Pbm1 and outputs the solenoid valve current Abm1 of the
calculated current value, and a processing that calculates a target
control amount for the 2nd directional control solenoid valve 52,
that is, the value of a current (solenoid valve current Abm2) to be
applied to the 2nd directional control solenoid valve 52 on the
basis of the value of the operation stroke Vbm2 obtained in the
processing Pbm1 and outputs the solenoid valve current Abm2 of the
calculated current value.

[0118]The controller 70 is, therefore, set to control the 1st
directional control solenoid valve 51, which produces the pilot pressure
BMU, and the 2nd directional control solenoid valve 52, which
produces the pilot pressure BMD, by outputting the solenoid valve
currents Abm1, Abm2 that correspond to the control signal from the boom
control lever device 80.

[0119]Processing which the controller 70 performs to control each of the
directional control solenoid valves other than the 1st, 2nd,
15th and 16th directional control solenoid valves 51, 52, 65,
66, that is, the 3rd-14th directional control solenoid valves
53-64 is also set similar to the above-mentioned processing illustrated
in FIG. 6. Described specifically, the controller 70 is set to control
the 3rd directional control solenoid valve 53, which produces the
pilot pressure BKC, and the 4th directional control solenoid valve
54, which produces the pilot pressure BKD, by outputting solenoid valve
currents Abk1, Abk2 that correspond to a control signal from the boom
control lever device 80. Further, the controller 70 is set to control the
5th and 7th directional control solenoid valves 55, 57, which
produce the pilot pressure AMC, and the 6th and 7th directional
control solenoid valves 56, 58, which produce the pilot pressure AMD, by
outputting solenoid valve currents Aam1, Aam2 that correspond to a
control signal from the arm control lever device 82. Furthermore, the
controller 70 is set to control the 9th directional control solenoid
valve 59, which produces the pilot pressure SR, and the 10th
directional control solenoid valve 60, which produces the pilot pressure
SL, by outputting solenoid valve currents As1, As2 that correspond to a
control signal from the swing control lever device 83. In addition, the
controller 70 is set to control the 11th directional control
solenoid valve 61, which produces the pilot pressure TRF, and the
12th directional control solenoid valve 62, which produces the pilot
pressure TRB, by outputting solenoid valve currents Atr1, Atr2 that
correspond to a control signal from the right travel control pedal device
84. Moreover, the controller 70 is set to control the 13th
directional control solenoid valve 63, which produces the pilot pressure
TLF, and the 14th directional control solenoid valve 64, which
produces the pilot pressure TLB, by outputting solenoid valve currents
At11, At12 that correspond to a control signal from the left travel
control pedal device 85.

[0120]It is to be noted that the controller 70 is set to perform the
control of the 7th and 8th directional control solenoid valves
57, 58 only when the mode is the backhoe mode, in other words, to set
both of the solenoid valve current Aam1, which is to be outputted to the
7th directional control solenoid valve 57, and the solenoid valve
current Aam2, which is to be outputted to the 8th directional
control solenoid valve 58, at 0 irrespective of the voltage value of the
control signal from the arm control lever device 82 when the mode is the
loader mode.

[0121]FIG. 7 is a diagram illustrating processing which the controller
depicted in FIG. 5 performs to control the 15th directional control
solenoid valve.

[0122]As illustrated in FIG. 7, the controller 70 is set to perform
processing Pdo1, Pdo2 when a control signal is inputted from the open
control lever device 86.

[0123]The processing Pdo1 comprises the processing that selectively
performs the first or second processing to be described next in (3) and
(4).

[0124](3) The first processing is the processing that, when the condition
that the voltage value of a control signal is 0 V or higher (control
signal≧0 (positive)) is satisfied, the voltage value of the
control signal is substituted for the value indicating the operation
stroke Vdo1 of the control pedal 86a upon the pivotal operation of the
control pedal 86a in the one direction from the neutral position
(operation stroke Vdo1=control signal, operation stroke Vod2=0 (zero)).

[0125](4) The second processing is the processing that, when the condition
that the voltage value of a control signal is lower than 0 (control
signal<0 (negative)) is satisfied, the absolute value (ABS) of the
voltage value of the control signal is substituted for the value
indicating the operation stroke Vdo2 of the control pedal 86a upon the
pivotal operation of the control pedal 86a in the other direction (the
direction opposite to the one direction) from the neutral position
(operation stroke Vdo1=0 (zero), operation stroke Vdo2=ABS (control
signal)).

[0126]The processing Pdo2 consists of a processing that calculates a
target control amount for the 15th directional control solenoid
valve 65 to produce the pilot pressure DO, that is, the value of a
current (solenoid valve current Ado) to be applied to the 15th
directional control solenoid valve 65 on the basis of the value of the
operation stroke Vdo2 obtained in the processing Pdo1 and outputs the
solenoid valve current Ado of the calculated current value.

[0127]In other words, the controller 70 is set to control the 15th
directional control solenoid valve 65 by outputting the solenoid valve
current Ado corresponding to only a control signal, specifically the
value of the operation stroke Vdo2 when the control pedal 86a of the open
control pedal device 86 is pivoted in the other direction. Processing
which the controller 70 performs to control the 16th directional
control solenoid valve 66 is set similar to the processing illustrated in
FIG. 7. Described specifically, the controller 70 is set to control the
16th directional control solenoid valve 66 by outputting a solenoid
valve current Adc corresponding to only a control signal when the control
pedal 87a of the close control pedal device 87 is pivoted in the other
direction. As the processing for controlling the 15th and 16th
directional control solenoid valves 65, 66 is set as described above, it
is possible to adopt an open control pedal device and a close control
pedal device of a construction similar to the right travel control pedal
device 84.

[0128]FIG. 8 is a diagram illustrating processing for controlling the
1st, 2nd and 3rd flow-rate control solenoid valves, said
processing being to be performed when the controller depicted in FIG. 5
is in the backhoe mode.

[0129]In this FIG. 8, the operation stroke Vbm1 is the voltage value of a
control signal outputted from the boom control lever device 80 when the
control lever 80a is pivotally operated in the one direction from the
neutral position as described using FIG. 6. On the other hand, the
operation stroke Vbm2 is the absolute value of the voltage value of a
control signal outputted from the boom control lever device 80 when the
control lever 80a is pivotally operated in the other direction (in the
direction opposite to the one direction) from the neutral position.

[0130]An operation stroke Vbk1 is the voltage value of a control signal
outputted from the bucket control lever device 81 when the control lever
81a is pivotally operated in the one direction from the neutral position.
An operation stroke Vbk2 indicates the absolute value of the voltage
value of a control signal outputted from the bucket control lever device
81 when the control lever 81a is pivotally operated in the other
direction from the neutral position.

[0131]An operation stroke Vam1 is the voltage value of a control signal
outputted from the arm control lever device 82 when the control lever 82a
is pivotally operated in the one direction from the neutral position. An
operation stroke Vam2 is the absolute value of the voltage value of a
control signal outputted from the arm control lever device 82 when the
control lever 82a is pivotally operated in the other direction from the
neutral position.

[0132]An operation stroke Vs1 is the voltage value of a control signal
outputted from the swing control lever device 83 when the control lever
83a is pivotally operated in the one direction from the neutral position.
An operation stroke Vs2 is the absolute value of the voltage value of a
control signal outputted from the swing control lever device 83 when the
control lever 83a is pivotally operated in the other direction from the
neutral position.

[0133]An operation stroke Vtr1 is the voltage value of a control signal
outputted from the right travel control pedal device 84 when the control
pedal 84a is pivotally operated in the one direction from the neutral
position. An operation stroke Vtr2 is the absolute value of the voltage
value of a control signal outputted from the right travel control pedal
device 84 when the control pedal 84a is pivotally operated in the other
direction from the neutral position.

[0134]An operation stroke Vt11 is the voltage value of a control signal
outputted from the left travel control pedal device 85 when the control
pedal 85a is pivotally operated in the one direction from the neutral
position. An operation stroke Vt12 is the absolute value of the voltage
value of a control signal outputted from the left travel control pedal
device 85 when the control pedal 85a is pivotally operated in the other
direction from the neutral position.

[0135]The controller 70 is set to perform processing Pb1-Pb6 shown in FIG.
8 at the time of the backhoe mode.

[0136]The processing Pb1 comprises the processing that detects operation
of the control lever or control pedal (operation direction and operation
stroke) of each of the boom control lever device 80, bucket control lever
device 81, arm control lever device 82, swing control lever device 83,
right travel control pedal device 84 and left travel control pedal device
85 on the basis of the value of the corresponding one of the operation
strokes Vbm1, Vbm2, Vbk1, Vbk2, Vam1, Vam2, Vs1, Vs2, Vtr1, Vtr2, Vt11,
Vt12.

[0137]The processing Pb2 comprises the processing that selectively
performs the first, second or third processing to be described next in
(5)-(7).

[0138](5) The first processing is the processing that, when the condition
that only the operation stroke Vam1 out of the operation strokes Vbm1,
Vbm2, Vbk1, Vbk2, Vam1, Vam2, Vs1, Vs2, Vtr1, Vtr2, Vt11, Vt12, that is,
all the operation strokes is greater than 0 (only Vam1>0) is
satisfied, in other words, when the operation detected in the processing
Pb1 is an instruction to extend the arm cylinder 208 singly, sets all of
the target control amounts of the pump flow rates to be controlled by the
respective 1st, 2nd and 3rd flow-rate control solenoid
valves 41, 42, 43, specifically target pump flow rates Q1, Q2, Q3 at a
pump flow rate Qa determined beforehand to be lower than a maximum pump
flow rate Qmax (Q1=Qa, Q2=Qa, Q3=Qa).

[0139](6) The second processing is the processing that, when the condition
that only the operation stroke Vbk1 out of all the operation strokes is
greater than 0 (only Vbk1>0) is satisfied, in other words, when the
operation detected in the processing Pb1 is an instruction to extend the
bucket cylinder 209 singly, sets all of the target control amounts Q1,
Q2, Q3 at Qa (Q1=Qa, Q2=Qa, Q3=Qa).

[0140]The target flow rate Qa mentioned in (5) and (6) is a value
empirically or experimentally determined for the purposes of inhibiting
an excess in the feed flow rate of pressure oil to the arm cylinder 208
when the arm cylinder 208 singly extends, that is, inhibiting an excess
in the operation speed of the arm 205 at the time of single arm-crowding
operation, and also preventing an excess in the feed flow rate of
pressure oil to the bucket cylinder 209 when the bucket cylinder 209
singly extends, that is, inhibiting an excess in the operation speed of
the bucket 206 at the time of single bucket-crowding operation.

[0141](7) The third processing is the processing that, when none of the
two conditions (only Vam1>0, only Vbk1>0) mentioned above in (5)
and (6) are satisfied, in other words, when the operation detected in the
processing Pb1 is neither an instruction to extend the arm cylinder 208
singly nor an instruction to extend the bucket cylinder 209 singly, sets
all of the target control amounts Q1, Q2, Q3 at the maximum pump flow
rate Qmax (Q1=Qmax, Q2=Qmax, Q3=Qmax).

[0142]The processing Pb3 comprises the processing that selects the largest
operation stroke (representative operation stroke Vmax) from all the
operation strokes.

[0143]The processing Pb4 comprises the processing that calculates the
target pump flow rates Q1, Q2, Q3 corresponding to the representative
operation stroke Vmax obtained in the processing Pb3. Described
specifically, functions that indicate correlations between the
representative operation stroke Vmax and the target pump flow rates Q1,
Q2, Q3 are stored beforehand in the controller 70, and the controller 70
is set such that the representative operation stroke Vmax is converted
into the target pump flow rates Q1, Q2, Q3 by using the functions.

[0145]The processing Pb6 comprises the processing that calculates the
values of respective solenoid valve currents Af1, Af2, Af3 of the
1st, 2nd and 3rd flow-rate control solenoid valves 41, 42,
43, said solenoid valve currents corresponding to a target pump flow rate
Qmin after the minimum comparison as selected in the processing Pb5, and
outputs all of the solenoid valve currents Af1, Af2, Af3 of the
calculated current values. Described specifically, functions that
indicate correlations between the target pump flow rates Q1, Q2, Q3 and
the solenoid valve currents Af1, Af2, Af3 are stored beforehand in the
controller 70, and the controller 70 is set such that the representative
target pump flow rates selected as the target pump flow rate Qmin are
converted into their corresponding solenoid valve currents Af1, Af2, Af3
by using the functions.

[0146]FIG. 9-1 is a diagram illustrating processing for controlling the
1st flow-rate control solenoid valve, said processing being to be
performed when the controller depicted in FIG. 5 is in the loader mode,
FIG. 9-2 is a diagram illustrating processing for controlling the
2nd flow-rate control solenoid valve, said processing being to be
performed when the controller depicted in FIG. 5 is in the loader mode,
and FIG. 9-3 is a diagram illustrating processing for controlling the
3nd flow-rate control solenoid valve, said processing being to be
performed when the controller depicted in FIG. 5 is in the loader mode.

[0147]In these FIGS. 9-1, 9-2 and 9-3, an operation stroke Vdo2 is the
absolute value of the voltage value of a control signal outputted from
the open control pedal device 86 when the control pedal 86a is pivotally
operated in the other direction from the neutral position as described
using FIG. 7. On the other hand, an operation stroke Vdc2 is the absolute
value of the voltage value of a control signal outputted from the close
control pedal device 87 when the control pedal 87a is pivotally operated
in the other direction from the neutral position.

[0148]The controller 70 is set to perform processing P11-P16 shown in FIG.
9-1 at the time of the loader mode.

[0149]The processing P11 comprises the processing that detects operation
of the control lever or control pedal (operation direction and operation
stroke) of each of the boom control lever device 80, bucket control lever
device 81, arm control lever device 82, swing control lever device 83,
right travel control pedal device 84, left travel control pedal device
85, open control pedal device 86 and close control pedal device 87 on the
basis of the value of the corresponding one of the operation strokes
Vbm1, Vbm2, Vbk1, Vbk2, Vam1, Vam2, Vs1, Vs2, Vtr1, Vtr2, Vt11, Vt12,
Vdo2, Vdc2.

[0150]The processing P12 comprises the processing that selectively
performs the first to tenth processing to be described next in (8)-(17).

[0151](8) The first processing is the processing that, when the condition
that only the operation stroke Vam1 out of the operation strokes Vbm1,
Vbm2, Vbk1, Vbk2, Vam1, Vam2, Vs1, Vs2, Vtr1, Vtr2, Vt11, Vt12, Vdo2,
Vdc2, that is, all the operation strokes is greater than 0 (only
Vam1>0) is satisfied, in other words, when the operation detected in
the processing P11 is an instruction to extend the arm cylinder 308
singly, sets the target control amount of the pump flow rates to be
controlled by the 1st flow-rate control solenoid valve 41,
specifically the target pump flow rate Q1 at a target pump flow rate Qb
determined beforehand to be lower than the maximum pump flow rate Qmax
(Q1=Qb).

[0152](9) The second processing is the processing that, when the condition
that only the operation stroke Vbk1 out of all the operation strokes is
greater than 0 (only Vbk1>0) is satisfied, in other words, when the
operation detected in the processing P11 is an instruction to extend the
bucket cylinder 309 singly, sets the target pump flow rate Q1 at Qb
(Q1=Qb).

[0153](10) The third processing is the processing that, when the condition
that only the operation strokes Vbk1, Vam1 out of all the operation
strokes are greater than 0 (only Vbk1, Vam1>0) is satisfied, in other
words, when the operation detected in the processing P11 is an
instruction to extend the bucket cylinder 309 and to extend the arm
cylinder 308 at the same time, sets the target pump flow rate Q1 at Qb
(Q1=Qb).

[0154](11) The fourth processing is the processing that, when the
condition that only the operation strokes Vbk1, Vam2 out of all the
operation strokes are greater than 0 (only Vbk1, Vam2>0) is satisfied,
in other words, when the operation detected in the processing P11 is an
instruction to extend the bucket cylinder 309 and to retract the arm
cylinder 308 at the same time, sets the target pump flow rate Q1 at Qb
(Q1=Qb).

[0155](12) The fifth processing is the processing that, when the condition
that only the operation strokes Vbk2, Vam1 out of all the operation
strokes are greater than 0 (only Vbk2, Vam1>0) is satisfied, in other
words, when the operation detected in the processing P11 is an
instruction to retract the bucket cylinder 309 and to extend the arm
cylinder 308 at the same time, sets the target pump flow rate Q1 at Qb
(Q1=Qb).

[0156](13) The sixth processing is the processing that, when the condition
that only the operation strokes Vbm1, Vam1 out of all the operation
strokes are greater than 0 (only Vbm1, Vam1>0) is satisfied, in other
words, when the operation detected in the processing P11 is an
instruction to extend the boom cylinder 307 and to extend the arm
cylinder 308 at the same time, sets the target pump flow rate Q1 at Qb
(Q1=Qb).

[0157](14) The seventh processing is the processing that, when the
condition that only the operation strokes Vbm2, Vam1 out of all the
operation strokes are greater than 0 (only Vbm2, Vam1>0) is satisfied,
in other words, when the operation detected in the processing P11 is an
instruction to retract the boom cylinder 307 and to extend the arm
cylinder 308 at the same time, sets the target pump flow rate Q1 at Qb
(Q1=Qb).

[0158](15) The eighth processing is the processing that, when the
condition that only the operation strokes Vam1, Vdo2 out of all the
operation strokes are greater than 0 (only Vam1, Vdo2>0) is satisfied,
in other words, when the operation detected in the processing P11 is an
instruction to extend the arm cylinder 308 and to retract the open/close
cylinder 313 at the same time, sets the target pump flow rate Q1 at Qb
(Q1=Qb).

[0159](16) The ninth processing is the processing that, when the condition
that only the operation strokes Vam1, Vdc2 out of all the operation
strokes are greater than 0 (only Vam1, Vdc2>0) is satisfied, in other
words, when the operation detected in the processing P11 is an
instruction to extend the arm cylinder 308 and to extend the open/close
cylinder 313 at the same time, sets the target pump flow rate Q1 at Qb
(Q1=Qb).

[0160]The target flow rate Qb mentioned in (10) to (16) is a value
empirically or experimentally determined for the purposes of inhibiting
an excess in the operation speed of the arm 305 at the time of single
arm-crowding operation (when only the arm cylinder 308 extends),
inhibiting an excess in the operation speed of the bucket 306 at the time
of single bucket-tilting operation (when only the bucket cylinder 309
extends), and also preventing excess(es) in the operation speed(s) of the
boom 305, arm 306 and/or bucket 307 and/or an excess in the open/close
speed of the bucket 306 at the time of specific combined operation of the
front working assembly 303.

[0161](17) The tenth processing is the processing that, when none of the
nine conditions mentioned above in (8) to (16) are satisfied, sets the
target pump flow rate Q1 at the maximum pump flow rate Qmax (Q1=Qmax).

[0162]The processing P13 comprises the processing that selects the largest
operation stroke (representative operation stroke Vmax1) from all the
operation strokes.

[0163]The processing P14 comprises the processing that calculates the
target pump flow rate Q1 corresponding to the representative operation
stroke Vmax1 obtained in the processing Pb13. Described specifically, a
function that indicates a correlation between the representative
operation stroke Vmax1 and the target pump flow rate Q1 is stored
beforehand in the controller 70, and the controller 70 is set such that
the representative operation stroke Vmax1 is converted into the target
pump flow rate Q1 by using the function.

[0164]The processing Pb15 comprises the processing that compares the
target pump flow rate (Q1=Qb or Q1=Qmax) set in the processing Pb12 with
the target pump flow rate Q1 calculated in the processing Pb14 and
selects the lower target pump flow rate.

[0165]The processing Pb16 comprises the processing that calculates the
value of the solenoid valve current Af1 of the 1st flow-rate control
solenoid valve 41, said solenoid valve current corresponding to the
target pump flow rate Qmin1 after the minimum comparison as selected in
the processing P15. Described specifically, a function that indicates a
correlation between the target pump flow rate Q1 and the solenoid valve
current Af1 is stored beforehand in the controller 70, and the controller
70 is set such that the target pump flow rate Q1 is converted into the
solenoid valve current Af1 by using the function.

[0166]The controller 70 is set to perform processing P17-P111 shown in
FIG. 9-2 at the time of the loader mode.

[0167]The processing P17 comprises the processing that sets the target
control amount of the pump flow rate controlled by the 2nd flow rate
control solenoid valve 42, namely the target pump flow rate Q2 at Qb or
Qmax by performing similar processing as in the above-mentioned second
processing P12 (Q2=Qb or Q2=Qmax).

[0168]The processing P18 comprises the processing that selects the largest
operation stroke (representative operation stroke Vmax2) from all the
operation strokes other than the operation strokes Vbk2, Vam2, Vs1, Vs2.

[0169]The processing P19 comprises the processing that calculates the
target pump flow rate Q2 corresponding to the representative operation
stroke Vmax2 obtained in the processing Pbl8. Described specifically, a
function that indicates a correlation between the representative
operation stroke Vmax2 and the target pump flow rate Q2 is stored
beforehand in the controller 70, and the controller 70 is set such that
the representative operation stroke Vmax2 is converted into the target
pump flow rate Q2 by using the function.

[0170]The processing Pb110 comprises the processing that compares the
target pump flow rate (Q2=Qb or Q2=Qmax) set in the processing Pb17 with
the target pump flow rate Q2 calculated in the processing Pb19 and
selects the lower target pump flow rate.

[0171]The processing Pb111 comprises the processing that calculates the
value of the solenoid valve current Af2 of the 2nd flow-rate control
solenoid valve 42, said solenoid valve current corresponding to the
target pump flow rate Qmin2) after the minimum comparison as selected in
the processing P110, and outputs the solenoid valve current Af2 of the
calculated current value. Described specifically, a function that
indicates a correlation between the target pump flow rate Q2 and the
solenoid valve current Af2 is stored beforehand in the controller 70, and
the controller 70 is set such that the target pump flow rate Q2 is
converted into the solenoid valve current Af2 by using the function.

[0172]The controller 70 is set to perform processing P12-P116 shown in
FIG. 9-3 at the time of the loader mode.

[0173]The processing P112 comprises the processing that sets the target
control amount of the pump flow rate controlled by the 3rd flow rate
control solenoid valve 43, namely the target pump flow rate Q3 at Qb or
Qmax by performing similar processing as in the above-mentioned second
processing P12 (Q3=Qb or Q3=Qmax).

[0174]The processing P113 comprises the processing that selects the
largest operation stroke (representative operation stroke Vmax3) from all
the operation strokes other than the operation strokes Vam2, Vs1, Vs2.

[0175]The processing P114 comprises the processing that calculates the
target pump flow rate Q3 corresponding to the representative operation
stroke Vmax3 obtained in the processing Pb113. Described specifically, a
function that indicates a correlation between the representative
operation stroke Vmax3 and the target pump flow rate Q3 is stored
beforehand in the controller 70, and the controller 70 is set such that
the representative operation stroke Vmax3 is converted into the target
pump flow rate Q3 by using the function.

[0176]The processing Pb115 comprises the processing that compares the
target pump flow rate (Q3=Qb or Q3=Qmax) set in the processing Pb112 with
the target pump flow rate Q3 calculated in the processing Pb114 and
selects the lower target pump flow rate (Qmin3).

[0177]The processing Pb116 comprises the processing that calculates the
value of the solenoid valve current Af3 of the 3rd flow-rate control
solenoid valve 43, said solenoid valve current corresponding to the
target pump flow rate Qmin3 after the minimum comparison as selected in
the processing P115. Described specifically, a function that indicates a
correlation between the target pump flow rate Q3 and the solenoid valve
current Af3 is stored beforehand in the controller 70, and the controller
70 is set such that the target pump flow rate Q3 is converted into the
solenoid valve current Af3 by using the function.

[0178]FIG. 10-1 a flowchart illustrating a routine when the controller
depicted in FIG. 5 controls the 1st, 2nd and 3rd flow-rate
control solenoid valves and 1st-16th directional control
solenoid valves, FIG. 10-2 is a continuation of the flowchart illustrated
in FIG. 10-1, and FIG. 11 shows diagrams which illustrate relations
between the states of the 1st and 2nd signal generation
circuits and the details shown on the display unit. Using these FIGS.
10-1, 10-2 and 11, operation of the first embodiment will be described.

[Backhoe Mode]

[0179]A description will be made about operation when the first embodiment
is mounted on the backhoe excavator 200.

[0180]In this case, the mode instruction means 71 is arranged on the
backhoe excavator 200, with the 1st connector being connected and
the 2nd connector being disconnected.

[0181]When the controller 70 is powered on, the controller is set in a
predetermined initial state, specifically is initialized (step S1), and
then reads a mode selection signal (step S2), as illustrated in FIG.
10-1. As the 1st connector and 2nd connector are now in the
connected state and disconnected state, respectively, in the mode
instruction means 71, the results of the reading of the mode selection
signal by the controller 70 become the results that the backhoe mode
selection signal B is ON and the loader mode selection signal L is OFF
("YES" in step S3). The controller 70 which has obtained the results sets
the mode setting value at a value predetermined corresponding to the
backhoe mode (step S5).

[0182]Further, the controller 70 outputs, to the display unit 72, an
instruction signal for displaying the results of the reading of the
backhoe mode selection signal and loader mode selection signal L,
specifically the results that only the backhoe mode selection signal B
has been read. As a consequence, the display unit 72 shows an image
notifying the results that only the backhoe mode selection signal B has
been read, in other words, that the mode is to be set this time in the
backhoe mode as illustrated in FIG. 11A.

[0183]As shown in FIG. 10-2, the controller 70 next performs input
processing of control signal(s) (step S8). As a consequence, operation
stroke (s) Vbm1, Vbm2, Vbk1, Vbk2, Vam1, Vam2, Vs1, Vs2, Vtr1, Vtr2, Vt11
and/or Vt12 is (are) obtained from control signal (s) of the boom control
lever device 80, bucket control lever device 81, arm control lever device
82, swing control lever device 83, right travel control pedal device 84
and/or left travel control pedal device 85. It is to be noted that the
open control pedal device 86 and close control pedal device 87 are
arranged on the loader excavator 300 and neither a control signal from
the open control pedal device 86 nor a control signal from the close
control pedal device 87 is not inputted into the controller 70 at the
present time.

[0184]The controller 70 then determines the currently-set mode from the
mode setting value when any one of the operation strokes Vbm1, Vbm2,
Vbk1, Vbk2, Vam1, Vam2, Vs1, Vs2, Vtr1, Vtr2, Vt11, Vt12 is greater than
0, in other words, upon detection of operation of at least one of the
boom control lever device 80, bucket control lever device 81, arm control
lever device 82, swing control lever device 83, right travel control
pedal device 84 and left travel control pedal device 85 (step S9). The
mode is determined to be the backhoe mode at the present time.

[0188]As a consequence, one or more of the solenoid valve currents Abm1,
Abm2, Abk1, Abk2, Aam1, Aam2, As1, As2, Atr1, Atr2, At11, At12, said one
or more solenoid valve currents having current values greater than 0, are
applied the corresponding one or ones of the 1st-16th
directional control solenoid valves 51-66 other than the 15th and
16th directional control solenoid valves 65, 66, specifically the
1st-14th directional control solenoid valves 51-64.

[0189]In the one or ones of the 1st-14th directional control
solenoid valves 51-64, to which the corresponding solenoid valve currents
have been applied, the valve position or positions of its or their main
valves are switched, and as a consequence, pilot pressure(s) is (are)
produced. The pilot pressure(s) is (are) applied to the corresponding one
or ones of the 1st-15th directional control valves 21-35 other
than the 8th directional control valve 28, namely the
1st-7th, 9th-15th directional control valves 21-27,
29-35 in the hydraulic circuit 1.

[0190]Described specifically, in the backhoe mode, the 1st-7th,
9th-15th directional control valves 21-27, 29-35 out of the
1st-15th directional control valves 21-35 are controlled in
accordance with operation of the boom control lever device 80, bucket
control lever device 81, arm control lever device 82, swing control lever
device 83, right travel control pedal device 84 and left travel control
pedal device 85, and the 8th directional control valve 28 does not
operate.

[0192]As a consequence, the solenoid valve currents Af1, Af2, Af2 are
applied to the 1st, 2nd and 3rd flow-rate control solenoid
valves 41, 42, 43. As a result, the pilot pressures i1, i3, i5, i6, i7,
i8 are applied from the 1st flow-rate control solenoid valve 41 to
the regulators 11a, 13a, 15a, 16a, 17a, 18a for the 1st, 3rd,
5th, 6th, 7th and 8th variable-displacement hydraulic
pumps 11, 13, 15, 16, 17, 18, respectively, the pilot pressure i2 is
applied from the 2nd flow-rate control solenoid valve 42 to the
regulator 12a for the 2nd variable-displacement hydraulic pump 12,
and the pilot pressure i4 is applied from the 3rd flow-rate control
solenoid valve 43 to the regulator 14a for the 4th
variable-displacement hydraulic pump 14.

[0193]As described using FIG. 8, the solenoid valve currents Af1, Af2, Af3
are all set at the same current value. Therefore, the pilot pressures i1,
i3, i5, i6, i7, i8 produced by the 1st flow-rate control solenoid
valve 41, the pilot pressure i2 produced by the 2nd
variable-displacement hydraulic pump 42 and the pilot pressure i4
produced by the 3rd variable-displacement hydraulic pump 43 take the
same pressure value. Namely, in the backhoe mode, the specification (the
flow rates required for driving the backhoe excavator) of the backhoe
excavator is met by evenly controlling the pump flow rates of all the
1st-8th variable-displacement hydraulic pumps 11-18 in
accordance with the operation of the boom control lever device 80, bucket
control lever device 81, arm control lever device 82, swing control lever
device 83, right travel control pedal device 84 and left travel control
pedal device 85.

[0194]Subsequent to the completion of the output processing, the
controller 70 causes the routine to return to step S8 (step
S13→step S8).

[0195]As a result of the performance of the control of the valve positions
of the respective 1st-7th and 9th-15th directional
control valves 21-27, 29-35 out of the 1st-15th directional
control valves 21-35 and the performance of the control of the pump flow
rates of all the 1st-8th variable-displacement hydraulic pumps
11-18 to the even value as described above, the hydraulic circuit 1
functions as a hydraulic drive circuit for backhoe excavator.

[Loader Mode]

[0196]A description will be made about operation when the first embodiment
is mounted on the loader excavator 300. In this case, the mode
instruction means 71 is arranged on the loader excavator 300, with the
1st connector being disconnected and the 2nd connector being
connected.

[0197]When the controller 70 is powered on, the controller is set in a
predetermined initial state, specifically is initialized (step S1), and
then reads a mode selection signal (step S2), as illustrated in FIG.
10-1. As the 1st connector and 2nd connector are now in the
disconnected state and connected state, respectively, in the mode
instruction means 71, the results of the reading of the mode selection
signal by the controller 70 become the results that the backhoe mode
selection signal B is OFF and the loader mode selection signal L is ON
("NO" in step S3→"YES" in step S4). The controller 70 which has
obtained the results sets the mode setting value at a value predetermined
corresponding to the loader mode (step S6).

[0198]Further, the controller 70 outputs, to the display unit 72, an
instruction signal for displaying the results of the reading of the
backhoe mode selection signal B and loader mode selection signal L,
specifically the results that only the loader mode selection signal L has
been read. As a consequence, the display unit 72 shows an image of
details corresponding to the results that only the loader mode selection
signal L has been read, in other words, an image to the effect that the
mode is to be set in the loader mode as illustrated in FIG. 11B.

[0200]The controller 70 then determines the currently-set mode from the
mode setting value when any one of the operation strokes Vbm1, Vbm2,
Vbk1, Vbk2, Vam1, Vam2, Vs1, Vs2, Vtr1, Vtr2, Vt11, Vt12, Vdo2, Vdc2 is
greater than 0, in other words, upon detection of operation of at least
one of the boom control lever device 80, bucket control lever device 81,
arm control lever device 82, swing control lever device 83, right travel
control pedal device 84, left travel control pedal device 85, open
control pedal device 86 and close control pedal device 87 (step S9). The
mode is determined to be the loader mode at the present time.

[0204]As a consequence, one or more of the solenoid valve currents Abm1,
Abm2, Abk1, Abk2, Aam1, Aam2, As1, As2, Atr1, Atr2, At11, At12, Ado, Adc,
said one or more solenoid valve currents having current values greater
than 0, are applied the corresponding one or ones of the
1st-16th directional control solenoid valves 51-66 other than
the 7th and 8th directional control solenoid valves 57, 58,
specifically the 1st-6th and 9th-16th directional
control solenoid valves 51-56, 59-66.

[0205]In the one or ones of the 1st-6th and 9th-16th
directional control solenoid valves 51-56, 59-66, to which the
corresponding solenoid valve currents have been applied, the valve
position or positions of its or their main valves are switched, and as a
consequence, pilot pressure(s) is (are) produced. The pilot pressure(s)
is (are) applied to the corresponding one or ones of the
1st-15th directional control valves 21-35 other than the
15th directional control valve 35, namely the 1st-14th
directional control valves 21-34 in the hydraulic circuit 1.

[0206]Described specifically, in the loader mode, the 1st-14th
directional control valves 21-34 are controlled in accordance with
operation (operation directions and operation strokes) of the boom
control lever device 80, bucket control lever device 81, arm control
lever device 82, swing control lever device 83, right travel control
pedal device 84, left travel control pedal device 85, open control pedal
device 86 and close control pedal device 87, and the 15th
directional control valve 35 does not operate.

[0208]As a consequence, the solenoid valve currents Aft, Af2, Af2 are
applied to the 1st, 2nd and 3rd flow-rate control solenoid
valves 41, 42, 43. As a result, the pilot pressures i1, i3, i5, i6, i7,
i8 are applied from the 1st flow-rate control solenoid valve 41 to
the regulators 11a, 13a, 15a, 16a, 17a, 18a for the 1st, 3rd,
5th, 6th, 7th and 8th variable-displacement hydraulic
pumps 11, 13, 15, 16, 17, 18, respectively, the pilot pressure i2 is
applied from the 2nd flow-rate control solenoid valve 42 to the
regulator 12a for the 2nd variable-displacement hydraulic pump 12,
and the pilot pressure i4 is applied from the 3rd flow-rate control
solenoid valve 43 to the regulator 14a for the 4th
variable-displacement hydraulic pump 14.

[0209]As described using FIGS. 9-1, 9-2 and 9-3, the current values of the
respective solenoid valve currents Af1, Af2, Af3 in the loader mode are
separately set. Therefore, the pilot pressures i1, i3, i5, i6, i7, i8
produced by the 1st flow-rate control solenoid valve 41, the pilot
pressure i2 produced by the 2nd variable-displacement hydraulic pump
12 and the pilot pressure i4 produced by the 3rd
variable-displacement hydraulic pump 43 are also set separately. Namely,
in the loader mode, the specification (the flow rates required for
driving the loader excavator) of the loader excavator is met by
individually controlling the pump flow rates of all the 1st,
3rd, 5th, 6th, 7th and 8th variable-displacement
hydraulic pumps 11, 13, 15-18, the pump flow rate of the 2nd
variable-displacement hydraulic pump 12 and the pump flow rate of the
4th variable-displacement hydraulic pump 14.

[0210]Subsequent to the completion of the output processing, the
controller 70 causes the routine to return to step S8 (step
S13→step S8).

[0211]As a result of the performance of the control of the valve positions
of the respective 1st-14th directional control valves 21-34 out
of the 1st-15th directional control valves 21-35 and the
performance of the individual control of the pump flow rates of all the
1st, 3rd, 5th, 6th, 7th and 8th
variable-displacement hydraulic pumps 11, 13, 15, 16, 17, 18, the pump
flow rate of the 2nd variable-displacement hydraulic pump 12 and the
pump flow rate of the 4th variable-displacement hydraulic pump 14 as
described above, the hydraulic circuit 1 functions as a hydraulic drive
circuit for loader excavator.

[Error Mode]

[0212]When there is a disconnection (including the situation that the
first and second connectors are both disconnected) or a short-circuit
(including the situation that the first connector and the second
connector are both connected) between the mode instruction means 71 and
the controller 70, there are obtained in step S2 the determination
results that the backhoe mode selection signal B and the loader mode
selection signal L are both OFF or the determination results that the
backhoe mode selection signal B and the loader mode selection signal L
are both ON ("NO" in step S3→"NO" in step S4). The controller 70
which has obtained the determination results sets the mode setting value
at a value predetermined corresponding to the error mode (step S7).

[0213]Further, the controller 70 outputs, to the display unit 72, an
instruction signal for displaying the results of the reading of the
backhoe mode selection signal and loader mode selection signal L. In the
case of the determination results that neither the backhoe mode selection
signal B nor the loader mode selection signal L was read, the display
unit 72 therefore shows an image of details corresponding to the
determination results, specifically, as shown in FIG. 11C, an image to
the effect that the mode is set in the error mode and to the effect that
a disconnection trouble has occurred. In the case of the determination
results that the backhoe mode selection signal B and the loader mode
selection signal L were both read, on the other hand, the display unit 72
shows an image of details corresponding to the determination results,
specifically, as shown in FIG. 11D, an image to the effect that the mode
is set in the error mode and to the effect that a disconnection trouble
has occurred.

[0214]As shown in FIG. 10-2, the controller 70 next performs input
processing of control signal(s) (step S8). The controller 70 then
determines the currently-set mode from the mode setting value when any
one of the operation strokes Vbm1, Vbm2, Vbk1, Vbk2, Vam1, Vam2, Vs1,
Vs2, Vtr1, Vtr2, Vt11, Vt12, Vdo, Vdc is greater than 0, in other words,
upon detection of operation of at least one of the boom control lever
device 80, bucket control lever device 81, arm control lever device 82,
swing control lever device 83, right travel control pedal device 84, left
travel control pedal device 85, open control pedal device 86 and close
control pedal device 87 (step S9). The mode is determined to be the error
mode at the present time.

[0215]In the error mode, the controller 70 next calculates the current
values of the respective solenoid valve currents Abm1, Abm2, Abk1, Abk2,
Aam1, Aam2, As1, As2, Atr1, Atr2, At11, At12, Ado, Adc, Af1, Af2, Af3
(step S11). Described specifically, the current values of the respective
solenoid valve currents Abm1, Abm2, Abk1, Abk2, Aam1, Aam2, As1, As2,
Atr1, Atr2, At11, At12, Ado, Adc, Af1, Af2, Af3 are set at 0 irrespective
of the magnitudes of the respective operation strokes Vbm1, Vbm2, Vbk1,
Vbk2, Vam1, Vam2, Vs1, Vs2, Vtr1, Vtr2, Vt11, Vt12, Vdo2, Vdc2 (step
S12). It is to be noted that, when the first embodiment is not mounted on
the backhoe excavator 200, the calculation of the solenoid valve currents
Ado, Adc is not performed because neither the open control pedal device
86 nor the close control pedal device 87 is connected to the controller
70.

[0218]Subsequent to the output processing, the controller 70 causes the
routine to return to step S8.

[0219]As the 1st-15th directional control valves 21-35 and
1st-8th variable-displacement hydraulic pumps 11-18 are
controlled as described above, the 1st-15th directional control
valves 21-34 and 1st-8th variable-displacement hydraulic pumps
11-18 are also maintained in inoperative states, irrespective of
operation of any one or more of the boom control lever device 80, bucket
control lever device 81, arm control lever device 82, swing control lever
device 83, right travel control pedal device 84, left travel control
pedal device 85, open control pedal device 86 and close control pedal
device 87, when the backhoe mode selection signal B and the loader mode
selection signal L are both OFF or when the backhoe mode selection signal
B and the loader mode selection signal L are both ON.

[0220]According to the first embodiment, the following advantages effects
can be obtained.

[0221]The first embodiment can selectively constitute a hydraulic drive
circuit for backhoe excavator or a hydraulic drive circuit for loader
excavator without changing the numbers and arrangements of
variable-displacement hydraulic pumps and directional control valves or
reassembling hydraulic hoses and hydraulic lines in the hydraulic circuit
1. By keeping the first connector connected and keeping the second
connector disconnected in the mode instruction means 71, specifically by
instructing the selection of the backhoe mode to the controller 70
through the mode instruction means 71, the control of the 1st,
2nd and 3rd flow-rate control solenoid valves 41, 42, 43 and
1st-16th directional control solenoid valves 51-66 can be
performed by the controller 70 such that the hydraulic circuit 1
functions as a hydraulic drive circuit for backhoe excavator. By keeping
the first connector disconnected and keeping the second connector
connected in the mode instruction means 71, specifically by instructing
the selection of the loader mode to the controller 70 through the mode
instruction means 71, on the other hand, the control of the 1st,
2nd and 3rd flow-rate control solenoid valves 41, 42, 43 and
1st-16th directional control solenoid valves 51-66 can be
performed by the controller 70 such that the hydraulic circuit 1
functions as a hydraulic drive circuit for loader excavator. Owing to the
foregoing, the first embodiment makes it possible to easily conduct the
change of the machine mode from one corresponding to the backhoe
excavator 200 to one corresponding to the loader excavator 300 or its
opposite change, and therefore, to reduce the labor required for the
above-described change work and also to shorten the time required for the
work.

[0222]In the first embodiment, the mode can be set in the backhoe mode by
bringing the second connector into the disconnected state while
maintaining the first connector in the connected state, and the mode can
also be set in the loader mode by bringing the second connector into the
connected state while maintaining the first connector in the disconnected
state. Specifically, the mode change can be conducted by simple work,
that is, by pulling out or pushing in the connectors, and therefore, the
mode can be changed with ease. Further, the 1st and 2nd signal
generation circuits 71a, 71b each of which includes both of the 1st
and 2nd connectors are electric circuits of simple construction, so
that a trouble can be readily found and maintenance can be performed with
ease.

[0223]In the first embodiment, the computer of the controller 70 is
configured to perform mode setting by performing reading of the backhoe
mode selection signal B and loader mode selection signal L only once
before the control of the 1st, 2nd and 3rd flow-rate
control solenoid valves 41, 42, 43 and the 1st-16th directional
control solenoid valves 51-66 are first initiated during from power on to
power off. As a consequence, it is possible to prevent a switch from the
backhoe mode to the loader mode or any switch from the loader mode to the
backhoe mode even when a disconnection or short-circuit occurs in the
1st signal generation circuit 71a or 2nd signal generation
circuit 71b during work by the hydraulic excavator. Namely, it is
possible to prevent a faulty operation of the hydraulic excavator which
would otherwise be caused by a disconnection or short-circuit in the
1st and 2nd signal generation circuits 71a, 71b.

[0224]In the first embodiment, it is possible to confirm, by taking a look
at an image shown on the display unit 72, whether or not the results of
reading of the backhoe selection signal and loader mode selection signal
by the computer of the controller 70 are consistent with the
corresponding results of the states of the first and second connectors.
The first embodiment can, therefore, contribute to the detection of
mix-up of the states of the first and second connectors corresponding to
each of the backhoe mode and loader mode and also to the detection of a
disconnection or short-circuit in the first or second signal generation
circuit.

Second Embodiment

[0225]A description will be made about a second embodiment.

[0226]FIG. 12 is a diagram illustrating a state that a hydraulic circuit
arranged in the second embodiment is connected to the boom cylinder, arm
cylinder and bucket cylinder in the front working assembly for the
backhoe excavator. FIG. 13 is a diagram showing a state that the
hydraulic circuit depicted in FIG. 12 is connected to the boom cylinder,
arm cylinder, bucket cylinder and open/close cylinder in the front
working assembly for the loader excavator.

[0227]The second embodiment is provided with a hydraulic circuit 101
depicted in FIGS. 12 and 13. This hydraulic circuit 101 is provided with
1st-6th variable-displacement hydraulic pumps 111-116 and
1st-12th directional control valves 121-132.

[0229]The 1st-12th directional control valves 121-132 are
grouped into a 1st valve group 106 comprised of the
1st-4th directional control valves 121-124, a 2nd valve
group 107 comprised of the 5th-8th directional control valves
125-128, and a 3rd valve group 108 comprised of the
9th-12th directional control valves 129-132.

[0230]To these 1st, 2nd and 3rd valve groups 106, 107, 108,
the 1st, 2nd and 3rd pump units 102, 103, 104 are
connected, respectively, via lines each of which combines together oils
delivered from the two variable-displacement hydraulic pumps that make up
the corresponding pump unit, that is, lines 136, 137, 138.

[0231]The 1st and 11th directional control valves 121, 131 are
arranged such that they can perform selective switching of flow rate and
flow direction of pressure oil corresponding to each of an extension and
a retraction of the bucket cylinder 209 arranged on the backhoe excavator
200 and selective switching of flow rate and flow direction of pressure
oil corresponding to each of an extension and a retraction of the bucket
cylinder 309 arranged on the loader excavator 300.

[0232]The 2nd and 12th directional control valves 122, 132 are
arranged such that they can perform selective switching of flow rate and
flow direction of pressure oil corresponding to each of an extension and
a retraction of the boom cylinder 207 arranged on the backhoe excavator
200 and selective switching of flow rate and flow direction of pressure
oil corresponding to each of an extension and a retraction of the boom
cylinder 307 arranged on the loader excavator 300.

[0233]The 3rd and 5th directional control valves 123, 125 are
arranged such that they can perform selective switching of flow rate and
flow direction of pressure oil corresponding to each of an extension and
a retraction of the arm cylinder 208 arranged on the backhoe excavator
200 and selective switching of flow rate and flow direction of pressure
oil corresponding to each of an extension and a retraction of the arm
cylinder 308 arranged on the loader excavator 300.

[0234]The 4th directional control valve 124 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to each of rotations in opposite two
directions of the left travel motor 210 arranged on the backhoe excavator
200 and selective switching of flow rate and flow direction of pressure
oil corresponding to each of rotations in opposite two directions of the
left travel motor 310 arranged on the loader excavator 300.

[0235]The 6th directional control valve 126 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to each of an extension and a retraction of
the bucket cylinder 209 arranged on the backhoe excavator 200 and
selective switching of flow rate and flow direction of pressure oil
corresponding to each of an extension and a retraction of the open/close
cylinder 313 arranged on the loader excavator 300.

[0236]The 7th directional control valve 127 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to an extension of the boom cylinder 207
arranged on the backhoe excavator 200 and selective switching of flow
rate and flow direction of pressure oil corresponding to each of an
extension of the boom cylinder 307 arranged on the loader excavator 300
and an extension of the bucket cylinder 309 arranged on the loader
excavator 300.

[0237]The 8th directional control valve 128 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to each of rotations in opposite two
directions of the right travel motor 212 arranged on the backhoe
excavator 200 and selective switching of flow rate and flow direction of
pressure oil corresponding to each of rotations in opposite two
directions of the right travel motor 312 arranged on the loader excavator
300.

[0238]The 9th directional control valve 129 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to each of rotations in opposite two
directions of the swing motor 211 arranged on the backhoe excavator 200
and selective switching of flow rate and flow direction of pressure oil
corresponding to each of rotations in opposite two directions of the
swing motor 311 arranged on the loader excavator 300.

[0239]The 10th directional control valve 130 is arranged such that it
can perform selective switching of flow rate and flow direction of
pressure oil corresponding to each of an extension and a retraction of
the arm cylinder 208 arranged on the backhoe excavator 200 and selective
switching of flow rate and flow direction of pressure oil corresponding
to only an extension out of the extension and a retraction of the arm
cylinder 308 arranged on the loader excavator 300.

[0240]FIG. 14 is a block diagram illustrating a system which the second
embodiment is provided with to control the hydraulic circuits shown in
FIGS. 12 and 13. In this FIG. 14, those equivalent to the corresponding
ones depicted in FIG. 5 are identified by the same signs as the signs
used in FIG. 5.

[0241]As depicted in FIG. 14, the second embodiment is provided with
plural flow-rate control solenoid valves, specifically 1st, 2nd
and 3rd flow-rate control solenoid valves 141, 142, 143 arranged
such that the pilot pressures i1-i6 can be applied to the regulators
11a-116a for the 1st-6th variable-displacement hydraulic pumps
111-116. The second embodiment is also provided with plural directional
control solenoid valves, specifically 1st-16th directional
control solenoid valves 151-166 arranged such that the pilot pressures
BMU, BMD, BKC, BKD, AMC, AMD, SR, SL, TRF, TRB, TLF, TLB, DO, DC can be
applied to the 1st-12th directional control valves 121-132. The
second embodiment is further provided with a pilot pump 173 as a
hydraulic pressure source for the pilot pressures i1-i6 and the pilot
pressures BMU, BMD, BKC, BKD, AMC, AMD, SR, SL, TRF, TRB, TLF, TLB, DO,
DC. The 1st, 2nd and 3rd flow-rate control solenoid valves
141, 142, 143 and the 1st-16th directional control solenoid
valves 151-166 are comprised of proportional solenoid control valves.

[0242]The 1st flow-rate control solenoid valve 141 is arranged such
that a pilot pressure can be applied to only the regulator 111a for the
1st variable-displacement hydraulic pump 111 out of the regulators
111a-116a for the 1st-6th variable-displacement hydraulic pumps
111-116. The 2nd flow-rate control solenoid valve 142 is arranged
such that pilot pressures can be applied to only the regulators 112a,
113a, 114a for the 2nd, 3rd and 4th variable-displacement
hydraulic pump 112, 113, 114 out of the regulators 111a-116a for the
1st-6th variable-displacement hydraulic pumps 111-116. The
3rd flow-rate control solenoid valve 143 is arranged such that pilot
pressures can be applied to only the regulators 115a, 116a for the
5th and 6th variable-displacement hydraulic pumps 115, 116 out
of the regulators 111a-116a for the 1st-6th
variable-displacement hydraulic pumps 111-116.

[0243]The 1st directional control solenoid valve 151 is arranged such
that the pilot pressure BMU can be applied to the 2nd, 7th and
12th directional control valves 121, 127, 132. The 2nd
directional control solenoid valve 152 is arranged such that the pilot
pressure BMD can be applied to the 2nd and 12th directional
control valves 122, 132.

[0244]The 3rd directional control solenoid valve 153 is arranged such
that the pilot pressure BKC can be applied to the 1st and 11th
directional control valves 121, 131. The 4th directional control
solenoid valve 154 is arranged such that the pilot pressure BKD can be
applied to the 1st and 11th directional control valves 121,
131.

[0245]The 5th directional control solenoid valve 155 is arranged such
that the pilot pressure BMD or BKC can be applied to the 7th
directional control valve 127.

[0246]The 6th directional control solenoid valve 156 is arranged such
that the pilot pressure AMC can be applied to the 3rd, 5th and
10th directional control solenoid valves 123, 125, 130. The 7th
directional control solenoid valve 157 is arranged such that the pilot
pressure AMD can be applied to the 3rd and 5th directional
control solenoid valves 123, 125.

[0247]The 8th directional control solenoid valve 158 is arranged such
that the pilot pressure AMD can be applied to the 10th directional
control solenoid valve 130.

[0248]The 9th directional control solenoid valve 159 is arranged such
that the pilot pressure SR can be applied to the 9th directional
control valve 129. The 10th directional control solenoid valve 160
is arranged such that the pilot pressure SL can be applied to the
9th directional control valve 129.

[0249]The 11th directional control solenoid valve 161 is arranged
such that the pilot pressure TRF can be applied to the 8th
directional control valve 128. The 12th directional control solenoid
valve 162 is arranged such that the pilot pressure TRB can be applied to
the 8th directional control valve 128.

[0250]The 13th directional control solenoid valve 163 is arranged
such that the pilot pressure TLF can be applied to the 4th
directional control valve 124. The 14th directional control solenoid
valve 164 is arranged such that the pilot pressure TLB can be applied to
the 4th directional control valve 124.

[0251]The 15th directional control solenoid valve 165 is arranged
such that the pilot pressure BK or DO can be applied to the 6th
directional control valve 126. The 16th directional control solenoid
valve 166 is arranged such that the pilot pressure BKD or DC can be
applied to the 6th directional control valve 126.

[0253]For the backhoe mode and for the loader mode, the controller 170 is
set the same with respect to the kinds of solenoid valve currents to be
applied to the 1st-4th, 6th, 7th, and
9th-14th directional control solenoid valves 151-154, 156, 157,
159-164, respectively. Described specifically, the controller is set to
apply the solenoid valve currents Abm1, Abm2, Abk1, Abk2, Aam1, Aam2, As
1, As2, Atr1, Atr2, At11, At12, Ado, Adc to the 1st-4th,
6th, 7th, and 9th-14th directional control solenoid
valves 151-154, 156, 157, 159-164, respectively.

[0254]With respect to the kinds of solenoid valve currents to be applied
to the 5th, 8th, 15th and 16th directional control
solenoid valves 155, 158, 165, 166, respectively, on the other hand, the
controller is set different between the backhoe mode and the loader mode.
Described specifically, the controller is set such that in the backhoe
mode, the solenoid valve current Abm2 is applied to the 5th
directional control solenoid valve 155, the solenoid valve current Aam2
is applied to the 8th directional control solenoid valve 158, the
solenoid valve current Abk1 is applied to the 15th directional
control solenoid valve 165, and the solenoid valve current Abk2 is
applied to the 16th directional control solenoid valve 166. In the
loader mode, on the other hand, the controller is set such that the
solenoid valve current Abk1 is applied to the 5th directional
control solenoid valve 155, no solenoid valve current is applied to the
8th directional control solenoid valve 158, the solenoid valve
current Ado is applied to the 15th directional control solenoid
valve 165, and the solenoid valve current Adc is applied to the 16th
directional control solenoid valve 166.

[0255]Concerning the setting of the controller 170 for the solenoid valve
current Af1, Af2, Af3 for controlling the 1st, 2nd and 3rd
flow-rate control solenoid valves 141, 142, 143 in the second embodiment,
a detailed description will be omitted. In the backhoe mode, however, the
controller is set to inhibit an excess in the operation speeds of the
bucket 206 and arm 205 during bucket-dumping operation or arm-crowding
operation. In the loader mode, on the other hand, the controller is set
to inhibit an excess in the operation speed of the arm 305 during
arm-crowding operation. This setting is suited for backhoe excavators and
loader excavators of specifications that the digging force and workload
are smaller than those required for the backhoe excavator 200 and loader
excavator 300 to which the first embodiment is applied.

[0256]According to the second embodiment, the following advantageous
effects can be obtained.

[0257]For similar reasons as in the first embodiment, the second
embodiment makes it possible to easily conduct the change of the machine
mode from one corresponding to a backhoe excavator to one corresponding
to a loader excavator or its opposite change. Therefore, it is possible
to reduce the labor required for the above-described change work and also
to shorten the time required for the work.

[0258]In particular, the second embodiment can be applied to models
required to meet digging force and workload smaller than those required
for the backhoe excavator 200 and loader excavator 300, that is, models
which are large hydraulic excavators but are smaller than the backhoe
excavator 200 and loader excavator 300, because the second embodiment is
provided with the hydraulic circuit 101 including fewer variable
displacement hydraulic pumps and directional control valves than the
hydraulic circuit 1 arranged in the first embodiment.

[0259]The first and second embodiments are each provided with the plural
flow-rate control solenoid valves as a pump flow-rate control means, the
directional control solenoid valves as a directional control means and
the controller as a regulation means such that control of the regulators
for the variable-displacement hydraulic pumps and the directional control
valves in the hydraulic circuit 1 or 101 can be realizing using
electronic control. It is, however, to be noted that the present
invention is not limited to such hydraulic circuits and that a hydraulic
circuit may be constructed to permit, with only hydraulic pilot
pressures, the realization of control of the regulators and directional
control valves in accordance with the control lever devices and control
pedal devices.

[0260]The first embodiment is, as mentioned above, provided with the
hydraulic circuit 1 including the eight variable-displacement hydraulic
pumps and fifteen directional control valves. The second embodiment is,
as mentioned above, provided with the hydraulic circuit 101 including the
twelve variable-displacement hydraulic pumps and twelve directional
control valves. These hydraulic circuits 1, 101 are examples of a
hydraulic circuit including at least two variable-displacement hydraulic
pumps and at least seven directional control valves, that is, examples of
a hydraulic circuit for a large hydraulic excavator, to which the present
invention can be applied. In other words, the hydraulic circuit to which
the present invention can be applied is not limited to the hydraulic
circuit 1 or 101, but can be any hydraulic circuit including at least two
variable-displacement hydraulic pumps and at least seven directional
control valves arranged on the revolving upperstructure of a large
hydraulic excavator such that a hydraulic drive circuit for backhoe
excavator or a hydraulic drive circuit for loader excavator can be
selectively constructed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0261]FIG. 1 A side view of a large backhoe excavator to which embodiments
of a hydraulic drive system of the present invention for a large
hydraulic excavator can be applied.

[0262]FIG. 2 A side view of a large loader excavator to which the
embodiments of the hydraulic drive system of the present invention for
the large hydraulic excavator can be applied.

[0263]FIG. 3 A diagram illustrating a state that a hydraulic circuit
arranged in a first embodiment of the hydraulic drive system of this
invention for the large hydraulic excavator is connected to a left travel
motor, a right travel motor, a swing motor, a boom cylinder, an arm
cylinder and a bucket cylinder arranged on the backhoe excavator.

[0264]FIG. 4 A diagram showing a state that the hydraulic circuit depicted
in FIG. 3 is connected to a left travel motor, a right travel motor, a
swing motor, a boom cylinder, an arm cylinder, a bucket cylinder and an
open/close cylinder arranged on the loader excavator.

[0265]FIG. 5 A block diagram illustrating a system which the first
embodiment is provided with to control the hydraulic circuits shown in
FIGS. 3 and 4.

[0266]FIG. 6 A diagram illustrating processing which a controller depicted
in FIG. 5 performs to control 1st and 2nd directional control
solenoid valves.

[0267]FIG. 7 A diagram illustrating processing which the controller
depicted in FIG. 5 performs to control a 15th directional control
solenoid valve.

[0268]FIG. 8 A diagram illustrating processing for controlling 1st,
2nd and 3rd flow-rate control solenoid valves, said processing
being to be performed when the controller depicted in FIG. 5 is in a
backhoe mode.

[0269]FIG. 9-1 A diagram illustrating processing for controlling the
1st flow-rate control solenoid valve, said processing being to be
performed when the controller depicted in FIG. 5 is a loader mode.

[0270]FIG. 9-2 A diagram illustrating processing for controlling the
2nd flow-rate control solenoid valve, said processing being to be
performed when the controller depicted in FIG. 5 is in the loader mode.

[0271]FIG. 9-3 A diagram illustrating processing for controlling the
3rd flow-rate control solenoid valve, said processing being to be
performed when the controller depicted in FIG. 5 is in the loader mode.

[0272]FIG. 10-1 A flowchart illustrating a routine when the controller
depicted in FIG. 5 controls the 1st, 2nd and 3rd flow-rate
control solenoid valves and 1st-16th directional control
solenoid valves.]

[0273]FIG. 10-2 A continuation of the flowchart illustrated in FIG. 10-1.

[0274]FIG. 11 Diagrams illustrating relations between the states of the
1st and 2nd signal generation circuits and details shown on a
display unit.

[0275]FIG. 12 A diagram illustrating a state that a hydraulic circuit
arranged in a second embodiment is connected to the boom cylinder, arm
cylinder and bucket cylinder in a front working assembly for the backhoe
excavator.

[0276]FIG. 13 A diagram showing a state that the hydraulic circuit
depicted in FIG. 12 is connected to the boom cylinder, arm cylinder,
bucket cylinder and open/close cylinder in a front working assembly for
the loader excavator.

[0277]FIG. 14 A block diagram illustrating a system which the second
embodiment is provided with to control the hydraulic circuits shown in
FIGS. 12 and 13.